Checking Maximum Hours for month

Question

For my application, system should allow user to enter maximum of 2 hours per month. 

 

Start date of month is 26th of every month and End date of the month is 25th of every month.

 

I want to check total hours between the period(26th - 25th). 

 

For example, 

 

For september month it should calculate from (26/08/2018 to 25/09/2018).

 

Kindly suggest best way to achieve this.

 

Thanks in advance.