On my second batch of beer I pitched the yeast and was shaking the carboy like crazy aerate it with the stopper in the top, I accidentally pushed on the stopper a bit too much sending it tumbling into the beer. Naturally I freaked out, my first thought was I have to get this thing covered asap, decided on foil over saran wrap because it was about 10:00 PM with work the next day, I wasn't going to be able to get a new plug until around 6:00PM after work.
I was really worried about it, I got off work a little early and made it to the shop before they closed, picked up about 5 of those plugs so I never ran into this situation again and went home, replaced the plug with the airlock and continued to worry over the next few weeks about what I had done to my poor, undeserving beer.
You'd never guess what happened though... The beer tasted perfect. It's like nothing had happened and it is sorta like the age old tale that you read time and time again, beer isn't as fragile as you think, just go with the flow because mistakes will happen. 20 hours with foil on top while active fermentation was ongoing and a rubber stopper inside it had no ill effects on the beer.
Best of luck to you, it'll turn out fine, my stopped popped right out when I was cleaning the carboy (well, I had to tug on it a little) and went right into the trash since obviously it was just a little too small.
