Yes, multiple procedures can be done at once. MY RULE is that no patient can be asleep for longer than 6 hours, and that is due to research that shows increased complications (such as blood clots) with longer surgeries. I will OFTEN do a tummy tuck with breast implants, or a facelift with upper eyelids, or a rhinoplasty and breast implants, or liposuction and a tummy tuck, etc.
The only rule is that the patient can't be asleep for longer than 6 hours.
Patients have tolerated anesthesia for 12-14-18 and even 20 hours in certain cases. Hand replantation and hand and face transplantation, for example, are procedures that take a very long time. In these rare cases, patients need to stay intubated (with the breathing tube) for overnight or into the next day as they recover.
My rule, though, is the 6 hour rule.