B.R.
If you can't make it until the morning, try to go atleast 4 hours. I ran into that similar problem with my son. I drank a regular glass of water at around 11pm and woke up around 4am and was able to get a positive...a week before my period was due. Be sure not to drink too much water because you may dilute your urine. I heard somewhere that the concentration of the hormone is elevated at around 4 hours of no voiding.
Good luck!