I've no experience whatsoever at drop catching, but I recently grabbed an expired one-word country level ccTLD in the dating niche, which was ideal for my regional traffic, and so I'm developing that now. I just happened to be looking in the right place at the right time.
The registrar, other drop bidders are important for very good names (manual drop catchers don't stand much of a chance for these domains) , but other domains you can try to bulk register yourself and pay basic registration fees. Exact time is not known but the time period is generally the same. For example , for .info , domains usually got deleted in a 10-15 minute period every day a few years ago.