Depends on your traffic volume, we drive enough that it takes at least 24 hours before it charts traffic, to see traffic from Monday I have to wait until early Wednesday :(
(sorry if you already know this & answered it in your previous comment. I just don't want others to miss out on GA's real time capability)
Officially they say that data won't appear until after 24 hours [1], but generally some of it will, but usually not all.
If you know the Analytics patterns of a site reasonably well (as I do my company's sites) then you can often look at the day's traffic and estimate how it's doing, but never expect it to be the final number.
(In some cases, I've actually seen traffic for the day go down after twenty four hours, once Analytics has finished working it out. I'm not sure why..)
[1] http://www.google.com/support/analytics/bin/answer.py?hl=en-...