I'm 15 days post op and wondering when it's safe to get into the gym and start a work out routine? Any suggestions?

My doctor had me out until 4 weeks before I could start slowly working into weight lifting and a gym routine. I would start cardio now and then ease into the true gym routine.

Though my doc had me walking a ton right away (I started with at least an hour every day,) they didn't want me doing anything else for about a month after surgery.

Thanks! I figured I would have to take it easy on the weights for a while but I didn't know if there were any limits on the cardio side like elliptical or bike?