Use it day and night, my only complaint is that after about a year something seems to go wrong with it, either the little hose leaks, the or the water pressure. I have owned several of the Waterpik devices. I still love them and need them.
I got this for Christmas and I used it and only works for a minute then I need to shut it off and then come back 5 mins a later. It will now take me 30 mins to brush and floss my teeth.
I purchased this to replace a Water Pik that I had for over 20 years. The new one has more features, runs quieter, and came with replacement irrigation and brushes. Love it. I use it twice a day as a substitute for flossing but still floss occasionally. About once a week I add a cap full of mouthwash with an alcohol base to help clean and disinfect the interior and exterior hoses. I do not have dentures but do have several crowns. The pulsating water keeps them clear of food.