Keys are required to open Gates, although any Key can open any Gate, i.e. there is no specific Key for a specific Gate.
Keys can be enveloped in Green Glow, meaning that when Tim grabs it his rewinding time will have it so he was holding it the whole time, until it is inserted into a Gate. After being inserted into a Gate a green Key cannot be taken back, and appears broken. If the gate is not green then rewinding the key insert will cause the gate to close, but the key to be broken. If the gate is green then both the key and the gate will be irreversibly stuck open.