There are no fixed numbers for this as preparing an aircraft involves so many factors - such as aircraft cleaning, cabin preparation, maintenance troubleshooting (if there is any), refuelling, etc. FMGS programming would only take 2-3 minutes (esp if there are company routes already stored in the database).
If the objective of your question is actually to know how to depart on time, the keyword here is just be systematic. You can actually do everything altogether and still have time to sip coffee while pax are boarding. In a nutshell, I would say just make the most of your time. Relax, don't rush, don't argue with the engineer or dispatch on company frequency, don't make unnecessary lengthy conversations with the ground staff and save the chitchat with the ladies on cruise. If you manage to keep everything in order then you will be able to depart on time.