RE: How much time does it take to restore Power platform enviornment
I agree with Daniel.
There are no fixed numbers for this. I've done it several times with various database sizes and concluded that there is no real conclusions to be made.
I understand that your client wants to know by forehand, but I can't give you a scientific answer. My experience is that it is usually quite fast, but not something you would sit around and wait for to be finished.
In practice you would not restore a production environment that often, because all the changes are reverted. My experience is that if just a part of the system needs to be restored, management does not restore the system because there will be so much data loss in the other part of the system.
Although my experience is that a complete restore could take up two hours I would not advise you to give any numbers to the client, because you cannot guarantee it. Instead note that both Microsoft and you will work as fast as possible and the likelihood that a complete restore will be necessary is very low.
Regards,
Timothy