It will take a maximum of 3 days for your upload to appear on the gallery. We validate submissions in 10, so that all get the equal chance to appear in the front page of the gallery. There are usually 2 or more updates in a day, which means at least 20 uploads are validated each day.
If however they do not appear, these are the reasons:
i) did not include a preview (applies to themes only)
ii) contains adult material
iii) file not up to threshold
If you are unsure if your file reach the validation list, you can always check your home page. If your file is validated, you can also check your homepage for statistics on your uploads.