Which system will my Miles be deducted from first, the time-based system or the activity-based system?

From 1 January 2020 onwards, Miles will be deducted on a first-in-first-out basis. In other words, Miles in the time-based system will be used up first.
When all Miles in the time-based system are used up, the Miles in the new activity-based system will be deducted.