luvcaroline, IMHO, yes. You will lose a lot of the experience sitting upstairs and not standing/dancing downstairs with most of the audience. This show is all about the "experience", so unless you have reason to not want - or be able - to stand for the required 90 minutes, definitely opt for the floor. It is crowded on the floor. Not painfully so, but you will standing with a crowd not that dissimilar to a dance floor at a popular club. The stage moves often and with it the audience, so you'll be moving a lot and even learn and be asked to dance a line dance.
As for time... The show runs only about 80 minutes, but exiting The Public, perhaps getting anything checked, etc. figure another 20 or so minutes. So, it is possible to catch an 8p show uptown.
I will say that I often like to have some time to take a show in and process the experience. This was especially true with HERE LIES LOVE. I live here and so I'm not in a rush to see as much as I can in a few days, so take that into consideration, too.
Anyway, enjoy the show, it is really a lot of fun. And, welcome to New York. Have a great stay!
ARTc3 formerly ARTc. Actually been a poster since 2004. My name isn't Art. Drop the "3" and say the signature and you'll understand.