I think this is actually a reason why any potential trade for Carmelo wouldn't be completed before the press conference. I'm sure the Rockets would like to give CP3 his day and not have to be distracted by another acquisition.
I feel like this is the ending of Spider-Man Homecoming. There is a press conference; Morey is Stark and Melo is... Spoiler
Sounds pretty dumb if you ask me. Can you imagine Morey telling the other teams, "Please wait for the trade to be completed because we want to introduce Paul first", then one day later, one of the teams changes their mind. Imagine losing a trade over something silly like that. I'm sure the explanation to Les would not go to well.
I'm expecting a "we want Melo / C-P-3!!" Chant like "let's go Cena / Cena sucks!" Too bad I'm an Oregon-based Rox fan. I'd totally be down for that.