I know some folks say "just 2 seconds, it's done" when they calibrate...
It's never been that case for me. I often have to hold it for a 20-count (15 seconds?) or more, and have to do that about 3-4 times.
As you can imagine it means no last-minute fiddling, and makes recalibrating after dropping half my bombs a pain.
I figured that was just the way it's coded, rather than it being a bug.