Do you train by mileage or time?

Ehh...

Races are set by distance. Humans have a poor intuitive sense of regulating effort over time but can instinctively govern their pace when told to race from the tall tree to the creek.

Train by distance. Adjust your pace to the conditions. Keep your mileage somewhere between 85-90 percent of what you think you could handle for that given week and you will have a good chance of long term success.

I agree. Running for time is a bad way to train. If you're looking at schools that do this, run the other way.

I do a lot of training on trails so I mostly train by time. I’d be depressed if I looked at my milesplits going up a mountain.

I do have set loops where I know the distance and just plan to go for a 7mi run, also.

so I guess both.
Time for long days or hilly days.

Distance for moderate runs and specific workouts.

time for recovery/easy days also because it’s easy to push yourself too hard if you’re going for a set distance

Neither, I just run.

smells like hogsgur to me

Time for easy runs, I’m often tempted to speed up to get the run over with faster.

Distance for track work/tempo runs/reps to hit target splits and better gauge progress

This is wise. I would also include long runs as a specific distance and not time. Especially if you’re training for a half, thon, or longer. You’ll easier cover the duration in timed runs for 5-10k training but not necessarily for the longer distances.

Meant to say distance not duration

I train running by mileage and biking by time