Taking full distance tri long rides outside: Adding duration necessary?

I’m in week 5 of the full distance triathlon plan mid volume and would like to start riding outside on the weekends. It seems well established that riding inside on a trainer is more time efficient due to the lack of coasting, and I wonder if anyone has experience adjusting this in the reverse and adding time to outside rides to get a similar training benefit as the plan calls for without accumulating too much fatigue and affecting subsequent workouts. I realize there are many variables such as terrain and climate so there likely is not a one size fits all answer.

I live in a very hilly area and will regularly have to go over the power target of the indoor workout to get up steep hills (current FTP ~210), but can also coast a fair amount. These surges seem to produce a different type of fatigue vs the steady state nature of riding inside on the trainer even if the eventual NP is similar. My A race is IM Wisconsin so this will be good training in the big picture, but I am worried about missing subsequent workouts or bucking the intended progression of the plan. I am also actively working on improving holding consistent power and up and down hills. I would like the adaptation from the outside rides but also want to make sure I go about it most efficiently so any input would be greatly appreciated!