Hello Hiewiloi54
After the exit of the customs area, you need about 10 minutes to go to the platforms of the station.
It is not recommended to buy Supersaver Tickets from the airport. If your flight is late, you cannot use them in later trains, you must buy new tickets. Saver Day Passes could be a better option, but they are not always available or more expensive as point-to-point tickets.
You have enough time in Martigny. The timetable to Verbier is only indicative. This is a continuous service with small gondolas.
Kind regards
Danhiel