With a 08:00 arrival you can expect to be kerbside in 30 minutes - if the plane is not sprayed, you are one of the first off tbe aircraft, walk fast to immigration, dont stop at duty free, use the SmartGate passport readers (and there is no queue,, have no checkrd bags, and are not held up at Customs (or stopped by the dog).

Allow another 30 min from exiting Customs to walk to the Transfer Bus, wait and travel. And security.

so 90 min is tight but doable. IMHO, not doable if you are not seated to be off the plane as soon as the door opens