There is nothing like "Marriage Leave". The only leave that employee gets is earned leave. The employee needs to manage his/her personal matters like marriage or otherwise, within this quota.
Roughly speaking for the 20 days of attendance, an employee becomes eligible to get a day's leave. Please note that Sunday is weekly off and it cannot be considered as leave. There are 365 days in a year. Of these 52 are Sundays and if you exclude these then the number of working days reduce to 313. Now there 10 closed holidays, which mandatorily to be given. If you exclude this then number of working days reduce to 303. If you divide by 20, it comes to 15. Therefore, each employee is eligible to take 15 days paid leave per annum. The purpose of the leave could be anything.
Notwithstanding my calculation given above, I recommend you checking the provisions of shops and establishment act or factories as applicable to your business establishment.
For example, many proprietorship companies are following this. Quantum of leave depends on company to company. In a proprietorship company I have earlier worked, is giving 2 weeks leave with pay if an employee (male/female) gets married while on service.