There’s no mention of how many maintenances or how long the game will be other then that it is necessary to do them as required in the fine print.
That the regular maintenance is weekly does not infer that that will be the only maintenance. For launches it is expected the game gets patched quite a lot as issues crop up to give everyone the best gameplay experiences (like the major AH lag issue that got resolved)
Atleast it says here at the time of writing:
https://eu.battle.net/support/en/help/article/000358479
That there will be a scheduled maintenance in advance, 10 hours ago and that it will last from 3 till 7 unavailable the entire duration.
Plus at the BNET launcher:
No matter when they will do the maintenance, it will always hit someone and their data says this is the best time to do it.