There's a huge variation with this, particularly since this surgery is often performed with liposuction of one or more areas of the body.
First of all, though, you have to decide if you're talking about actual operating time (the time from the first incision until the dressing is applied or the last suture is placed) the time in the OR (which includes set-up and some recovery) or all of the above plus time in recovery.
Strictly speaking, surgical time is usually from about 2.5-4 hours, depending on exactly what has to be done (a "tummy tuck" after significant weight loss cannot reasonably be compared to a small tummy tuck after one pregnancy in which very little weight was gained, etc). 1-3 hours can be added for liposuction and additional tissue removal including the back, etc. So the total is typically about 2.5-5 hours - although surgeons operate at different speeds...and there's no prize for finishing first...
I hope that this helps, and good luck,