Hey OP, others have answered your question pretty well. In the future, please do try to approach your threads more from a philosophically Harm-Reduction-oriented place. We just don't like for our image to imply that we are all here to get as fucked up as possible, as fast as possible. We have a lot of registered members, sure, but think about all of the un-registered folk who just stop in occasionally and anonymously. No harm done, just giving you the primer!
So, Benzodiazepines are tricky and everyone needs to respect their potential to cause serious mayhem. The devil fools with the best laid plans as they say, and to that end, anyone is capable of accidentally blacking out and burning their house down trying to make a grilled cheese.
If you are inexperienced with Benzodiazepines, then I would not exceed 1mg Alprazolam (Xanax) or equivalent. I can almost guarantee that this dose will not cause blackout. Benzodiazepines, however, lower inhibitions anyway, so there is always the possibility of making a social faux paw and you definitely should not drive a car.
You will be feeling the full effects of the drug approximately one hour after you ingest the Alprazolam. If you want to redose at this point, you can. Just be aware, blackout is not something that most people plan on enduring, it's accidental. Everybody is different, but I can give you my experience as a general reference point. I am a guy that seems to have a naturally high tolerance to most drugs. I have no idea why. I can drink more, take more drugs etc.
1mg Alprazolam, I would barely even feel in a subjective sense. If I'm looking for true anxiety relief, I would take 3mg Alprazolam. If I take 4mg. the situation becomes unpredictable. As I've said, this is all relative, but I think myself and the other BL'ers here here have given you some pretty good points of reference from which to approach your usage.