Here will depend on which route you are taking .each route has different time to reach the top.
Machame route 6 -7 days
Marangu route 6 -days
Lemosho route 7-8days
Rongai route 6-7 days
Shira plateau route 7-8 days
Umbwe route 5-6 days
Northern circuit route 8-9 days