Most of geostationary satellites are launched at geostationary transfer orbit (GTO) first by rocket's upper stage. Than satellites separate and circularize the orbit by own propulsion. The upper stage is left at GTO - an elliptical orbit, usually with parameters like 180-200 km high at perigee, 35000 km high at apogee. The final stage's burn is performed at perigee to maximize efficiency because of Oberth effect.
The orbit of an upper stage will decay because of low perigee due to atmospheric drag. My question is: how much time GTO stages usually spend in the orbit before reentry? Months? years? decades?
In this anwer Falcon-9 stage reentered less than 4 months after launch. Is this lifetime typical?
Is any statistics available about GTO stages lifetimes?