This is my opinion.
Monthly Salary = the month salary = Base Salary
Rate per day = Base Salary / 26 day
Rate per hour = Base Salary / 208 hours
If employee would like to encash, it will be based on calendar day in a month. So, if May is 31 days, then the calculation as follows:-
Balance Leave Encashment = (Base Pay / 31 days) * Leave Balance.
Alternatively, you should refer to the employment agreement, how to compute the overtime rate as a guideline.