Hi lewis

you can make a schedule for this from

 settings-- > scheduler --- >  scheduled Actions

create an template in

 settings-- > emails --- >  template

create a model (object) and create function in that model (object), fuction should be like this

 def my_function(self,cr,uid,context=None):
     # search your created template id here ex: your_tem_id
     # search your model ids here  with your codition  ex: my_ids
     self.pool.get('email.tempalte').send_mail(self, cr, uid, your_tem_id, my_ids, force_send=True)
     return True

note: in schedule actions you will have to give your model object in object field and my_function in fucntion field and in parameter field ()

Thanks
Sandeep