Hi Ingo. THe distance is about 35km. There is a very efficient Volvo bus service called Vayu Vajra which you can board just outisde the arrival terminal. Look out for the Red couloured fancy buses with BIAS boards in the front. There is a regular service to the old airport from the new airport which will drop you at Leel Hotel. In the evening it might take you about 75 to 90 minutes. Hope this helps you.
Catch Red Color VOLVO Bus with no BIAS-4 or BIAS-6 outside airport. It is approximately 36 to 40 Km from Leela Palace and will take 45 minutes to 1.30 hr depends which time you are travelling.