In two places I've looked, it says that Hermir Strong-Heart is the common-level trainer for Heavy Armor. However, she has no such options for training at 1:00ish in the day.

Is it the wrong time of day? Or am I cut off from her training because I sided with the Imperials? She's said no such thing about my allegiances in her dialog bits...

Bump. I'm having the same issue. I didn't side with the imperials either. Need to find a heavy armor trainer.

There is the smith in the Orc stronghold south east of Markath (can't remember the name of the encampment). She is an expert trainer in Heavy Armor and I haven't had any trouble getting her to train me when she is around the forge. Maybe give her a try if you're friendly with the Orcs.

Thanks. I'll give her a shot.