Should we move to a Perth Airport hotel before an early flight?

Work backwards from the airline's bag-drop deadline and confirm the pickup time. Keep a backup transport option for the morning.

For a one-night transit stay, check the first shuttle, exact terminal served and late check-in. A nominal airport hotel can still require a taxi.

If you already have a Perth hotel, compare a prebooked car from there with the cost and hassle of moving rooms. A short airport distance is not the only factor.