The Drunken Lizard Pub

How is the number of rounds required to swap equipment sets determined? I've seen mine um from 1-2 to 4 and would like to get it back down

It is determined by the number of pieces you need to swap. Less difference between them, less rounds it takes to do.

I believe it's a round per item swapped out. I'm not 100% on that though.

From what I've seen it's the picking up of an item that costs the round, not the undoing of an item.

It is the number of items that changes. Count the differences between your current equipment and your preset.