When i am at my lab, i would like to plan a print on a specific time.
For example, the print duration is 7 hours, i would like to start the print at 1 am (then i am at home in my bed 
). Then i know the print is finished at 8 am when i start my day at the lab.
Is it possible to create this feature in preform / dashboard?
Assuming you know the possibility to prime a Form 3/3B so you can start a print remotely, there is no such timing feature (yet?).
Out of curiosity: Would starting a print in the evening be an alternative? You would have the advantage of most liquid resin having dropped off the finished print by the time you arrive and also it would be finished for sure even if it takes a bit longer than predicted. And as you know the print remains in the green state in the printer so you will not have any quality problem.
This is an interesting idea and I’d be happy to pass it along! That being said, I might echo what @Dim3nsioneer said above. Prints are perfectly happy sitting in the printer finished for a couple hours and as mentioned, that can give the part extra time to drain. I’ve left parts hanging over the weekend before and haven’t seen any ill-effects when I come in on Monday.
All that isn’t to say your request isn’t valid! Just offering some potential guidance based on your needs. 
For me, having the printer in a home office type scenario, I’d want to load the print job at night and have it kick off automatically around 6-7am.
The F3 makes a bit too much noise to have running around light sleepers, even at the other end of the house and behind two closed doors.
Starting it around the time the household is getting up to run a print job during the day, without me having to remember to hit the go button while in my pre-coffee state would be great. For most of what I print, the part would be ready and waiting for finishing when I get home.
This would be a great feature!