Oxygen in fermenter?

Started a 4gal batch of cider not more than 48 hours ago. When I moved the fermenter from my kitchen to a closet last night (8 hours ago), I caused the 3-piece airlock to suck-back too much vodka. I didn't notice it until this morning.

So my fermenter hasn't been properly air-locked for about ~8hours. It wasn't totally exposed compared to an open bottle, but the floating piece of the airlock wasn't floating. I refilled it and it's bubbling like normal.

Did I do any damage?

None whatsoever.

-a.

You are just fine. Some people even leave the lid loose on their buckets during the initial fermentation without problems. My bucket lid doesn't seal very well anymore, to the point that the airlock hardly bubbles, and still I manage to make good beer.

Yes you did damage, you wasted a tablespoon of vodka!

Seriously, not likely. The only thing that you could have done is suck some bacteria in when you sucked in the vodka and that isn't likely at all. Now that your yeast is busy eating sugars and excreting carbon dioxide, your airlock isn't even necessary. The escaping carbon dioxide will keep anything from getting in.

Probably not.
1) Yeast need oxygen at the start of fermentation and 2) you have some indication that fermentation has started,. If the airlock is bubbling, you have CO2 generation and any oxygen in the headspace has been displaced by the CO2.

When you really need to worry about oxidizing your brew is after fermentation is well under way or complete, and even then it would be along the lines of aerating your cider not just drying out the airlock or opening it to check gravity.

I think it's fine. RDWHAHB (it's what I'd do in your shoes.)

cool. thanks. Would rum work just as well in the airlock?

If you can keep it in the airlock, yes.
If you are going to drain it into your brew, it will have a much bigger flavor impact than vodka.

-a.