The time taken to climb Mount Kilimanjaro completely depends according to the Kilimanjaro routes and also your fitness level. The recommended days are 8 and 9 days via Lemosho Route, Northern circuit Route, or any of the Kilimanjaro routes.
Longer the days, more are your chances for a successful summit. You get more time for acclimatization, sleep on the lower elevations, and spend more time in the mountains.
The minimum time of 5 days should be considered for climbing Mount Kilimanjaro. This should be followed to keep yourself on a safer side. However, an additional day for better acclimatization is recommended.