I'd see no reason not to have the scope mounted before the rifle is ever fired. Is the person slated to do the mounting and sighting in experienced in both? Be aware that the eye relief that works for one shooter may not be perfect for another. The recoil of a 7 mag can be a bit snappy, so it might be wise to check your personal hold and eye relief before shooting for the first time.
One other thing I do like to do, especially with new rifles, is to make sure I check tightness of everything after returning from the first range session. It seems that it is not at all unusual to see some additional tightening needed after a rifle is first fired with a new mounting system installed.