I have a marriage certificate. Do I need to see the date of the wedding reception?

Amitabha! Of course, when you get married, you should choose an auspicious day and hold a banquet according to folk customs. However, according to your introduction, you just want to invite colleagues and classmates to get together on this grounds, and if you are not going to hold any ceremony, you don't have to be too particular. Considering that your classmates and colleagues will have things to study or work, you can give priority to the weekend when everyone is resting, and arrange a treat when the time is loose, so that it will be convenient for you and the invited guests. Don't you think?