That would be amusing. From memory I'm not sure how the sequencing works out but I'd imagine that you CAN actually do that. I think Omega opens up after the Citadel coup attempt by Cerberus. Although Traynor's 'game night' email is before that (or around the same time) you obviously don't have to take her up on it straight away.
You can actually do Omega as early as prior to Sur'Kesh. After Palaven, talk to Aria in Purgatory, and you should get the meet her at Dock 42 email upon your return to the Normandy. Probably the best time to do it story flow wise, right after you unite the mercenary groups for her. That's what I did on my current vanguard playthrough. One minor thing I noticed is that if you haven't picked up that one Turian assault rifle on Tuchanka yet, you can find it in Omega.