You can easily do Panama City in 5 days tops. The canal, casco viejo, amador causeway, monkey island, clubbing/dining etcStrange, I was there for nearly a week and felt that wasn't even close to being enough time and I did quite a few things. I'm hoping to be there for two weeks next time.
If you gonna do 2 weeks in Panama i highly suggest checking out some of the provinces that border Costa Rica