All of my snakes are different, thus have different trigger times. But they all strike and coil within seconds to a minute of putting the prey item into their tubs.
For live, I wouldn't leave a prey item alone with the snake for longer than 30 minutes max. After 30 minutes, pull out the prey and wait to feed again next week.
Hungry and scared rats/mice = potentially dangerous animals.
A hungry adult rat will eat your snake when left alone too long.
Depending on your snakes' feeding response, if he has a strong response, I would just start off with trying f/t.