No Going Back now. 70 LT-1

[Too Many Projects]

A red, Scotch Brite pad would have scuffed the flash off sufficiently to paint. Not understanding why you used the ospho after blasting ? There are others on this forum who use SPI far more than me, but once I have a part that has been blasted I clean and go straight to epoxy. I've never used ospho after reading about adhesion failures if it isn't thoroughly neutralized and then you deal with the flash rust issue.
Anyway, I don't see waiting more than 4 hours for the epoxy to induce. If you want to spray at night, mix the epoxy in the morning. The Black settles out quite a bit while sitting and I find stirring it after 2 hours helps with that and actually, rarely, wait any longer than 2 hours to use it.
1 pint isn't going to get you 2-3 coats IMO. A frame has a lot more area than we realize. I turn the fan pattern down a lot to minimize overspray paint loss and then the volume needs to be turned down as well, or it is easy to flood the part unless you are really moving the gun quickly. Difficult to spot spray into the channels with too much volume too. I believe you'll need a full quart to get good coverage and I would also add 10% medium reducer to get it to flow better.
Allow plenty of flash time between coats too, 1 hour is, usually, safe and helps prevent "excessive flowage" as my mentor calls runs... LOL
Are you a member on the SPI forum ? Those guys can advise you far better than I can with my limited experience. Member SMS on this forum has extensive experience with SPI as well.
1 other item I would like to suggest and it would take time for you to acquire, would be to use a liner system for the paint gun versus the cup. With a collapsible liner, you can paint upside down and not have paint running out of the vent hole in the cup cap.

Most of all, work on being patient with yourself and the process. Once mixed, the paint has a long window in a sealed container and there is no need to rush, even though we tend to feel we need to do that...