Hey,
why not setting a bool after you pressed F. F.e. its called bLightOn.
Start State is -> light is dark
Press F -> set bLightOn to true (or invert it with a NOT)
Play your timeline based on that bool -> so put branch with bLightOn value, if true Play Timeline if not Reverse Timeline,
if you dont want to toggle during a timeline loop then you could take your timeline variable and check if “Timeline->isPlaying” if yes, dont do something if not play regarding your bLightOn bool.
cheers