For me in NA, it is: Earn 35000 XP by Monday 5/31, 7:20AM. To get a garage slot.
3 days, 35K XP. Am I missing something or is that insane?
The upside is the intermediate bonuses are great. Missions for tier 8-9, or tier 10: Be in top 10 in 3 battles to get 10K battle XP (repeatable).
Just forget about the bonus mission.