Back when I had real teeth, I used the trays all night, as directed. I put a drop of the fluoride in each tooth segment of the tray and then put it in my mouth. Lot of good that did me (grin). I think the recommendations now are for the shorter periods. The dentist who made my trays was not very experienced with people about to get rad. Edd, the trays pressing on your tender gums could certainly be causing the bleeding. It would seem reasonable to me to follow a shorter schedule as long as you are consistent about doing it.