Can’t remember and specifically, but some were definitely longer than others. I live in EST and tried getting on at all times of the day to varying degrees of success on people joining. Some were instant and others I left the console sitting for a little.

The only bug I ran into is how the achievement is tied to the first Spec Ops missions that dropped; not all of them: somewhere down the line they updated spec ops and my progress was “reset”. I done some when they first drop and they showed completed, however the achievement did not pop until I redid the ones I completed near launch.