Blue light glasses are safe, according to many studies. In fact, they preserve your eyes by reducing eye strain and keeping your natural sleep levels in check. Blue light itself is not harmful in low quantities and at earlier times in the day. Later in the day, however, it affects your eyes and can lower your sleep quality.
Night Owl glasses can be worn as often as needed - there's no issue with wearing them all the time. They are most impactful, however, in the evening and closer to bed time, as this is when our eyes need greater protection from blue light.