In Breaking Bad Walter White hired Jack Welker to kill all of Mike's men along with their lawyer, Dan Wachsberger. Jack said he could have them all killed, but not within a 2 minute interval. Walter insisted they kill all during that time.
Why 2 minutes? Why not 10 minutes? Why not an hour? Why not a whole day?
If the men were killed over a few days, somebody might figure out that everyone associated with Mike was targeted and then move some of them into solitary confinement to protect them. But that would take time. Even if Mike's men were killed over 1 day, Jack's henchmen could probably get them all since the men (not counting the lawyer) were incarcerated in 3 different jails and it would take time for the authorities in 3 different jurisdictions to realize what was up.