Tibet trips

my estimated schedule is as follows (no tickets booket yet):
• Friday 4/4 arrive in Beijing
• Saturday + Sunday sightseeing
• Sunday 6/4 21:30 leave Beijing West Railway Station
• Tuesday 8/4 20:58 arrival in Lhasa
• Wednesday –Saturday in Tibet
• Sunday 13/4 flight back to Chengdu around 10
So i will have effectively 4 days in Tibet.
is there any advice on this schedule or can we just use this schedule to have a trip to Tibet with your service?