Is this still current? From IST to Taksim area (e.g. Grand Hyatt)? How long does the journey take, for instance, on a Thursday starting at around 18:15 from the airport?

Apparently there is also the Havaist bus line 16 to Taksim, which takes 90 minutes (2 stops en route) for 35 TL (USD2.10). That sounds like a long ride for the 48 km journey...