JT posted a vid Sunday that confirmed reports he was performing at Super Bowl LII, with his and Jimmy's mini skit playing on the phrase "have the time" ... which quickly morphed into "You're doing the halftime show at the Super Bowl??!!"

As we reported ... the rest of 'NSYNC could possibly join Justin onstage during his performance, which seems even likelier now that he's definitely got the gig.

Can't say the same for Janet Jackson, though. She was recently mum on rumors about a possible reunion, ya know ... after 2004 and all.

We got this feeling ... there probably ain't gonna be a next time.