Degus are diurnal, this basically means they're active in the daytime and sleep at night. This is controlled by their Circadian Rhythm which is for the most part influenced by daylight as well as their owner's activity (meaning this can be controlled by your actions). If you stay awake until 5am then they probably will do too, although it isn't a good idea.
Healthy degus will benefit from a strict structure of sleep, for instance the room they're in having the light turned off at the same time each night. If you have a dimmer switch in this room, it is a good idea to turn down the light slowly over a period of time to mimic the setting of the sun and to turn it off about an hour before you want them to sleep, especially if there are other light sources in the room (TV, Computer, bedside lamp etc). Remember, in the wild the "light" is dimmed at the same time every night
Once the lights are all off, the degus will engage in a little quiet chittering for a bit, and talking back to them in a calm quiet voice is both soothing for them and for you (helps with bonding) although it isn't important. Even if they fall asleep while you're talking, your talk should not disturb them. Most of this chittering is them trying to get comfortable and deciding who sleeps where.
If a degu doesn't get enough sleep he or she will become irritable, much like humans, and won't be much fun to be with...not good for their companions or for you.