If it goes through the entire drop process, you should know the very next day by looking in Whois.
Beware, If your looking to register a garbage domain like "britneywinkedatme.com" that has zero traffic, dont expect it to drop, drop catchers like Snapnames are grabbbing these drops, putting them up for auction, and when it doesnt sell, they release it, if it has traffic and showing profit, they keep them!.