I was under the impression the complete day cycle was in hours. So a 0.5 day cycle would actually be 15 minutes day and 15 minutes night. I have my server set to 2 hour day cycles, and there seems to be 1 hour of day for every 1 hour of night. I could be wrong though. So I'll quote Maegfaer and say don't quote me on it
Edit: So as far as crops go, they progress to the next growth stage every in-game day. If your day cycle is 2, then they grow every 2 hours. Even at that rate, you're looking at around 12-18 hours in real life before harvesting.