Measure intake first
The most likely explanation is lack of adequate intake of fluids during those hours.
You should measure your fluid intake for 24 hours and if it's less than 2 quarts or less than 8 glasses
(8 ounce glass) you are drinking less than recommended per day. Of course if you lose water perspiring, etc you may need more. You also ingest fluids when you eat fruits. If your fluid intake is normal get tested.