All night long is ok. Sometimes if I stay all night at a friends, they stay on, because I don't use timers. The plants don't care.
Side note: I was at a friend's house showing one of my blue spot lights. After about 5 minutes it went dead.
WTF? ?
I don't think the chinese guy I bought it from cares, so I'm not going to try to get a refund. ERRR!