Dunk a cotton swab into the LN2 and hold it against Mr. Wart. I’m not a dematologist, and I wasn’t timing the doc when he did my wart, so I really don’t know for how long. This will probably vary on the wart itself - whether it’s one that popped up last week and is still “fresh” or one that’s been on your foot for so long that you can claim it as a dependent on your income tax. Hopefully someone else here has been paying attention and can offer guidance on the time to freeze one.
As you appear to have easy access to LN2, it’s probably better to underfreeze and need a re-treatment than to overfreeze and damage otherwise healthy skin.
I just have to comment that the home freezing kits are well neigh useless. I froze the thing far more than I was supposed to and it didn’t do a damn thing. The little acid patches didn’t work either (followed the instructions exactly and ended up using up the whole box of 'em). Of course this was a plantars wart which are much harder to get rid of. I think the problem with the freezing chemical is that to be effective it must be very dangerous and they would get sued to pieces quickly when someone misuses it.
What finally worked for me was that I got fed up and deeply cut the MFer. I would let it heal, and of course it would come back a little, then I’d cut it again. About the third time did it. Those things go deep.