Flew to Dar a couple of months ago for a Medevac flight, we went to pick up a patient to take him to Joburg, with a PC12; landed at 22:00 and when I went to Flight Briefing office to pay the fees and file the outbound FP I was told that I have to wait until sunrise to leave...I then asked why I was granted permission to enter their airspace with a SET at night, so they call the Airport Safety Manager and she sent us an email after 15' granting permission for our departure as soon as possible because of Medevac flight...