Answer:
It flies when it's on and floats coming off.
Always wax, yet always wane: I melt, succumbed to the flame. Lighting darkness, with fate unblest, I soon devolve to shapeless mess.
Goes over all the hills and hollows. Bites hard, but never swallows.
My first is nothing but a name; my second is more small; my whole is of so little fame it has no name at all.
What measures out time. Until in time all is smashed to it?
If it’s information you seek, come and see me. If it’s pairs of letters you need, I have consecutively three. What am I?