gender reveal party- when should we have it?

Ta
So I am 13 weeks and three days today with my first baby. My husband got the results of our blood test for the gender. We are planning on doing a gender party for just our families and maybe a couple close friends. I work every other weekend so my options are only half available for dates. We are going to bar b que, play some guessing games then celebrate after we finally reveal. No gifts, it's just a celebration. 
My husband is planning the party. He is so excited. 
My husband wants to do it march 4th which I will be 21 weeks. I was thinking the sooner the better. Feb. 4th I will be 17 weeks. I won't get to find out till the party. He is going to surprise all of us. He wants to wait till the next ultrasound just to be sure it's 100% correct. 
He is already teasing saying i better pick a good name for 'him' cause 'she' is going to be beautiful. I don't know how long I can wait. I'm so excited also. 
My question is....... what is the appropriate time? Does it have to be after the 20 week ultrasound? Is 17 weeks too early?