Hello,
Activate Developer mode from general settings.
Go to Settings>Technical>Scheduled Actions.

Check for this scheduled action, this action is responsible for doing this job.

Here you can see the Next Execution Date, and interval as 'Execute Every'.

[Update]
So when this action runs based on the schedule, it will call the _update_accrual() method.
​

First part of that method.
​In this method, Odoo takes all the allocations that have nextcall(is a date) set as False or nextcall is less than today along with many other conditions.

When we create a new allocation, nextcall will be False. and odoo will reset nextcall based on the interval(Day/Week/Month) 

So in your case,

You created allocation on 14th Jan, if you created the allocation before 18:00:59, Your allocations nextcall will be on 14th Feb. else Your nextcall will be 15th Feb. 

 You can use 'Run manually' button to run this action manually when ever you wish.