Here is a way to cause the As Of date to immediately be modified when edit mode is entered:

  - a new FieldAutoJS widget that runs javascript from the xml when it becomes editable
  - declare a new writable field with create and write hooks that clear any attempted writes
  - include the field invisibly on the form and use the autojs widget to set any value
  - in onchange for the new field, if the field is not set, do whatever actions desired to initialize the form, e.g. set date

Javascript:

// 13.0.6.13.2-t8 jimays
// code--1299-edc6-4d86f0db-acb0-f9ee6cefae13--13.0.6.13.2-t8--7.55.20--5.22--XYqqm7*iTnaBOodPqhvqh1
//---------------------------------------------------------------------------------------------

odoo.define('carlisleofficesuites.thermostats', function (require){
    'use strict';
    var form_widget = require('web.form_widgets');
    var core = require('web.core');

    // gratitude https://www.odoo.com/forum/help-1/question/equivalent-javascript-onload-it-is-possible-when-form-is-loaded-75863
    // gratitude https://www.odoo.com/forum/aide-1/question/how-to-customize-the-onclick-javascript-action-of-an-edit-button-odoo-10-125253
    // gratitude https://www.odoo.com/fr_FR/forum/aide-1/question/onchange-method-works-before-something-change-on-field-odoo11-133024
    // gratitude https://stackoverflow.com/questions/7650071/is-there-a-way-to-create-a-function-from-a-string-with-javascript
    // gratitude https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function
    // which precisely asks the question, and also
    // gratitude https://stackoverflow.com/questions/31187456/which-method-is-called-when-user-click-on-edit-button
    // gratitude https://stackoverflow.com/questions/11970035/change-field-value-and-trigger-onchange-event-on-button-press
    // gratitude https://www.odoo.com/forum/aide-1/question/how-to-trigger-an-action-onload-of-a-form-view-23593
    // gratitude https://www.odoo.com/forum/help-1/question/override-a-field-s-value-on-form-load-108986
    // gratitude https://www.odoo.com/forum/aide-1/question/default-method-trigger-my-api-onchange-method-why-151042
    //  "Since a default value is being loaded..., there is a change in value which will trigger the onchange method.
    //   So whenever the value in that field changes, even when the default value is loaded, it will trigger the onchange method."
    //  "Try creating a new invisible field without any value. In your onchange check whether this field is empty or not.
    //   If it is empty, write some value to this field and exit. If it is not empty continue with your onchange.
    //   I mentioned this because this is easy to understand. There may be better ways to accomplish the same thing."
    // gratitude https://www.odoo.com/forum/aide-1/question/onchange-method-works-before-something-change-on-field-odoo11-133024
    //   "... when form is load, onchange method is automatically called."
    // gratitude http://elico-corp.com.sg/2015/10/01/how-to-tech-dynamically-modify-your-view/
    // gratitude https://stackoverflow.com/questions/39424027/adding-a-button-in-tree-view-odoo-8
    // gratitude addons/web/static/src/js/views/form_view.js
    // gratitude addons/web/static/src/js/views/form_widgets.js
    // gratitude FieldsBoolean and FieldsPriority and FieldBinaryFile
    //
    // Pair with:
    //
    //    <field name="auto" widget="autojs" autojs="your_function();"/?
    //
    // To force an onchange when Edit is clicked, field can add invisible="1" to the xml
    // Couple this code with create and write hooks that always clear the field from the write vals.
    //
    //    <field name="auto" widget="autojs" autojs="return 'auto';" invisible="1"/>
    // 
    //      as_of = fields.Datetime('As Of', required=True)
    //      auto = fields.Char('Auto')
    //
    //      @api.onchange('auto')
    //      def onchange_auto(self):
    //          if not self.auto:
    //              # the as_of is visibly adjusted when Edit is clicked
    //              self.as_of = fields.datetime.now()
    //
    //      @api.model
    //      def update_write_vals(self, vals):
    //          vals['as_of'] = fields.Datetime.now()
    //          if 'auto' in vals:
    //              del vals['auto']
    //
    //      @api.model
    //      @api.returns('self', lambda value: value.id)
    //      def create(self, vals):
    //          self.update_write_vals(vals)
    //          return super(ThisModel, self).create(vals)
    // 
    //      @api.multi
    //      def write(self, vals):
    //          self.update_write_vals(vals)
    //          super(ThisModel, self).write(vals)

    var FieldAutoJS = form_widget.FieldChar.extend({
        start: function(){
            true && console.log('FieldAuto.start: this.field: ' + JSON.stringify(this.field));
            true && console.log('FieldAuto.start: this.options.model_field: ' + JSON.stringify(this.options.model_field));
            var self = this;
            var change_effective_readonly = function(){
                if(!self.get("effective_readonly")){
                    true && console.log('FieldAuto: Auto field has become editable.');
                    if('autojs' in self.node.attrs){
                        true && console.log('FieldAuto: Setting value with javascript: ' + self.node.attrs.autojs);
                        var autojs_function = new Function(self.node.attrs.autojs);
                        var newValue = autojs_function(self);
                        var oldValue = self.get_value();
                        true && console.log('FieldAuto: Triggering change:value, oldValue: ' + oldValue + ', newValue: ' + newValue);
                        self.trigger("change:value", self, { oldValue: oldValue, newValue: newValue });
                        self.render_value();
                    }
                }
            };
            this.on("change:effective_readonly", this, change_effective_readonly);
            change_effective_readonly.call(this);
            this._super.apply(this, arguments);
        },
    });

    core.form_widget_registry.add('autojs', FieldAutoJS);

});

Python

class CarlisleOfficeSuites_Thermostat(models.Model):
    _name = 'carlisleofficesuites.thermostat'
    _rec_name = 'zone'

    zone = fields.Char('Zone', required=True)

    # 13.0.6.13.2-t8 The auto field is always blank in the database and always auto-set by the javascript upon entering form view edit mode.
    # This trick makes the form have a changed value as soon as it opens for edit, which visibly pre-adjusts the As Of, which is cute,
    # and more importantly marks the form as changed so a save actually calls the write hook, and the latest draft settings become active.

    as_of = fields.Datetime('As Of', required=True)
    auto = fields.Char('Auto')

    @api.onchange('auto')
    def onchange_auto(self):
	_logger.debug('onchange_auto, self.auto: ' + unicode(self.auto))
	if not self.auto:
​	    # the as_of is visibly adjusted when Edit is clicked
            self.as_of = fields.datetime.now()

    @api.model
    def update_write_vals(self, vals):
	vals['as_of'] = fields.Datetime.now()
	if 'auto' in vals:
	    del vals['auto']

    @api.model
    @api.returns('self', lambda value: value.id)
    def create(self, vals):
	self.update_write_vals(vals)
        return super(CarlisleOfficeSuites_Thermostat, self).create(vals)        
 
    @api.multi
    def write(self, vals):
	self.update_write_vals(vals)
	super(CarlisleOfficeSuites_Thermostat, self).write(vals)	
        return True

Did you try: 1. apply this patch - https://github.com/odoo/odoo/commit/2067a206ecba9a8dbf7f76a55926be964e580e7e 2. move your xxx before yyy_ids in form view 3. set _defaults for xxx to False Didn't check that, but that should work - if not, maybe change in logic (defaults = True) so that this field does change it's value.