Can a Facelift and tummy tuck be done at the same time?

If your surgeon is able to do both procedures expertly in a reasonable amount of time then yes.  Some surgeons are technically more adept than others in keeping operative times down.  Shorter operative times are associated with less complications in many series.  Discuss this with your surgeon

Depending on your health this is not a real problem. The combination of procedures would be fairly uncommon at least in my practice but I have done this. The advantage is that there will be one period of convalescence. The abdominoplasty is much more physiologically significant in the facelift.

A facelift and tummy tuck are two time consuming operations that require great attention to detail.  In my opinion and practice the two are not performed together.