Date twins!!! I just ordered my invitations last night and put June 12th as the rsvp date. My count is due into the venue 2 weeks after that so I figured it would give me time to chase people down that didn't RSVP.
I would as the venue/vendor when they need the final count and then decide. I would make it a bit earlier than they say because you will for sure have stragglers. I set my date October 1st and only got 7 of the 75 I sent out. Then I got one two days after the wedding without their name lol
I would say the 1st or 2nd week of June. It ultimately depends on when your venue needs your final count. My wedding is February 29, 2020 and we are asking for our RSVP's to be returned by January 15, 2020. Our wedding venue does not need our final count until 2 weeks prior to the wedding so I figure that gives me plenty of time to get the remainder of the RSVPs from any of my guests who wait until last minute to send them. It also gives me more time to make my seating chart.