I need to install quarter round that if flexible, what hints and tips do I need to be aware of. Such as: do I need to leave it in the room for a day or so before its installed?
If it's flex-trim, no it doesn't need to acclimate to the room, because it's a resin. Be careful nailing it. Unless using 18 ga. brads, pre-drill the holes so: a) it doesn't break; b) it doesn't give you raised "pimples" at the nail holes.
I assume I can then used a Brad Nailer to attach. What about bending around a radius, do I need to work it slowly to let it take shape? It should arrive in about a week will let you know how it went.
If it was ordered with a specific radius, it will be simplicity itself to install. But if a straight piece, yes, be careful, you could break it if bent beyond what it will take. That's why you order it with the desired curve in mind. Heat may not really help it bend, but cold could cause it to break easier.