1 to 4 sounds rather optimistic to me.
I've seen 1.5 times (60 minutes turbo equivalent to 90 minutes on the road) mentioned, probably in relation to TrainerRoad, and that I would tend to agree with, well especially if you are doing an ERG workout, as the resistance is controlled, there is no free wheeling, and no easing off the power, you have to hit the targets or you grind to a halt and fail.
For me to ride on a trainer for a longer amount of time, I need a bit of left to right movement, and not just a bike locked into a 100% static position - front to back is useful, but not as important - also key to get up out of the saddle from time to time, and even more key to have decent shorts, and the same style saddle as you ride outside.
If I'm doing a workout, I'll likely have something to watch on another screen, either drama, or sporting event, pretty much always on catch up.
If I'm in a Rouvy race or group ride, then I'll focus on that fully, and you need to in a race if you want to stay in a group.