T8<>T1 was 15mins from my experience. There are no separate road lanes but I've also never experienced traffic into T8 or T1 (or T7 or T5) or entering JFK (the bus took a long route, basically going to federal circle and back.)
I don't know about T4<>T1 specifically or T4 traffic. But with the length of your layover I would not stress over it.