Actually, it’s really not that hard to tell the night time from the day. Generally, going outside is usually enough to make it clear. If it’s dark, it’s night; if it’s light, it’s day: simple. Sure, some days will be overcast, but if there’s any remaining doubt, you can cross-check against the time of day, and it shouldn’t be that hard to work it out.
If you’re still experiencing difficulties, I recommend cutting back on the cocaine.