beginner question on contamination/hydrometer reading

I apologize if these are stupid questions, but...

Brewing my first batch and am curious about contamination. From all I've read, you want to prevent contamination (airborne/insufficient sanitazion, etc). On the other hand, you want to also take a hydrometer reading in order to ensure that fermentation is done which requires that you open the bucket (I'm using a bucket with lid for my primary). Obviously, I want to be pretty quick about it, so I'm going to have to carefully lift the lid, drop in the thief (to about the middle of the bucket?) siphon out some beer (can I call it beer at this stage?) and close in up. I'll repeat on the next day or the day after. If my readings on the hydrometer remain consistant, I'm going to transfer to a secondary (glass carboy).

So, I guess my question is this: When I read about contamination or the production of off flavors resulting from "air pollution" how long of an exposure are we talking? Am I going to get off flavors during the minute or so that I have to open the bucket to get the sample for a hydrometer reading or from exposure during transfer to a secondary? While I don't think this is the case, I'm wondering if I can get a ball park estimate as to what amount of time people generally consider excessive.

One other question: I'm preparing to sanitize my secondary (glass carboy). I'm using a no-rinse sanitizer that came with the kit. I'm going to fill up the carboy add the sanitizer and brush the carboy. I imagine I'd want to have it dry before I do the transfer (after pouring out the sanitizing water), but doesn't leaving it to dry run the risk of something airborne settling in it? Does it matter if there are a few water droplets in the carboy before transfer?

Appreciate the help!

Good sanitation is definitely important, but beer is pretty resilient.

When you want to take a sample for an sg reading, you just sanitize the thief and then pull your sample. Then close up the bucket, read the sample, and then drink it. Most things that will infect your beer aren't airborne, but bacteria and wild yeasts that are on surfaces. If you disinfect anything that touches the beer, you'll be fine.

When you sanitize your carboy, all you have to do is clean it first. Make sure it's clean to your eye and rinsed well. Then you can sanitize it by mixing up a gallon or so of water and your no rinse sanitizer, and slosh it all around, coating all the surfaces. No need to brush that. Then drain, and that's it. If you're using a no-rinse sanitizer, there is no need to dry it. Just rack the beer into it. Make sure you sanitize your bung and airlock as well.

1) Dude don't worry about air contamination...aslong as your work area is clean and you don't have **** that could fall in your wort from the celling I wouldn't worry at all...when I test my beer the lid is off for atleast 5-10 minutes and I've never had one problem.

2)Just leave a little bit of the sanitizer at the bottom over the carboy and put some saran wrap over the top to keep anything out. When I transfer to my secondary I dump out the left over star san I leave in the bottom and re-sanitize it again right before I transfer from the primary.

Hope this helps you out

Thank you both for your replys! Hopefully, my thieved beer will taste ok!