I believe it depends on the merchant. Most merchants are instant, but some are hours or even days. It just really depends. Obviously, most are instant, though. My balance always updates before my "today" stats do as well.
Commission Detail reports are generally 1-2 hours behind (for example, transactions made during the entire 8:00 hour usually post to the Detail report at 10:00). Performance reports are a few hours behind that. Advertisers that send in batch data (usually once per day) can take longer, of course.