Even at 5AM with no traffic it would be difficult to make it to the Levent metro station in 5 minutes. During any reasonable time of day it could take you 15-30 mins by taxi (it is practically impossible to walk and would take you forever if you did). As Maslak is currently a massive construction zone (developments, plus a bunch of highway/flyover work AND Metro digging)and the home of a new shopping center, it could seriously take you over an hour minimum to get from Levent to Maslak.