I don't think Glest should have some other "day" ingame. I often found that confusing in other games (taking Oblivion for example, I'd have to bring up a dialogue to get the time of the day often, though you could "rest" without penalty to change the time easily). Regardless, Glest shouldn't use that, and as Silnarm mentioned, days are not of set length. For example, in Military, a day is 600 seconds, or 10 minutes, instead of 1000 seconds, or 16 minutes and 40 seconds (the reason for this is because 10 minutes is easier to keep track of than 1000 seconds / 16:40.