So I may be starting a new job in a couple of months

I have a business trip to help open a new restaurant of our franchise in Louisiana in late-May. Pretty much, I'm working 6 9-hour days for two weeks plus a 9 hour drive there and 9 hour drive back. Not to mention, I'm being paid overtime for that, get free food, free housing, plus a $320 check just for going (well, technically for any things I'd need down there, but it's up to me to use).

After that, I have a job offer from an old boss of mine (restaurant's almost identical to the one I work at now, just simplified and more niche). I'll be starting at 2 dollars more than I'm making now and be an assistant manager of a new one opening up at the end of the year for salary (I did the math. Roughly $6.65 more than I'm making now).

The problem is, my current manager has mentioned making me a shift supervisor and eventually a manager within the next two years...but that's not a sure thing and even if the shift supervisor pay is more than what I'll start at the new place, I'm pretty sure manager pay would be less than what would it be at the new restaurant...so I'm definitely taking the job.

I JUST DON'T KNOW HOW TO TELL MY CURRENT MANAGERS. They love me. They freaked out when I almost had to quit last year and that was before considering promoting me. Should I tell them now in advance or wait until before I leave (I'd give them more than a two-week notice, but still).

HELP ME, KHV