Training outside or in a bike trainer?

Hi, and welcome to BT!

I do the vast majority of my training on an indoor trainer (for safety and weather reasons) and I typically just do what the workout states - one thing I've noticed over the years is that the neuro-muscular adaptation you develop indoors where you're constantly pedaling translates outdoors really noticeably.  

I think at this point, most training plans assume you're doing a bunch indoors with the proliferation of smart trainers, Zwift, etc.  ETA:  if you're using one of BT's plans, then they were designed years ago so they're probably effort or HR zone based.

If you're finding those indoor workouts are a little too challenging, you could back them down intensity or duration.  Two hours is about my limit for tolerating the indoor training on a bike.