There have been multiple countdowns so far.
Either they are fake decoys and there is only one real one (The booms? How many boom events so far? What happens when the 6th occurs?) occuring "behind the scenes" in a larger timeframe or yet to occur.
Or they are distinct countdowns pertaining to sub-operations. Single arrests, or perhaps the booms? Or just important movement cues?
The timing of his tweets might indicate how close the enemy is to reacting to the operation.
As the operation starts, 1hr posts mean they are relatively clear for operations.
30 minutes means the enemy knows something is going on.
10 minutes means the enemy is acting and organizing to counter the operation.
5 minutes means they need to get out of Dodge before the baddies show up with reinforcements.
Any off-time interval posts means that operation status has changed. Some for the better, others for worse.
That's my guess. Take it or leave it.