If you've issued a kill command, you now have to wait for the rollback to complete. That can take as long, and sometimes longer, than the original transaction. So, if the original transaction took 3 hours, then you issued a kill statement, you will have to wait probably at least 3 hours. This depends on a ton of factors such as how much data was moved, was the cause of the original long transaction due to large data movements or blocking or resource contention. All those factors could cause the rollback to go up or down.
You can get a quick look at what the rollback is doing, and if it's being blocked, by querying sys.dm_exec_requests.