NXT(which this is a fork of) uses a deadline system for its POS system. If I recall correctly it figures out how long it will be until elapsed time * balance maintained over the last 24 hours will become larger than a value derived from hashing information from the previous block with the public key holding that balance.
Interesting. I never bothered looking at NXT much. I dislike Java. I'll have to find a good overview somewhere, thanks.
I know ltc testnet and such use time-based deadlines on difficulty, as well, but that is slightly different.
