IIRC @Jonathan has said on the podcast that he trains on rollers. Ive not got the skill to, especially for sharp sprinty stuff, but I would spend hours on them pre and in lockdown on more stable state stuff. When I changed to resistance rollers it was certainly more engaging but that would be with artificial course (RGT which was better/ cheaper than Zwift but is no more). I wouldn’t be confident to spend more than 1 minute on them now.
Edit: There’s been a few threads on the topic of rollers for training, a quick search brings up this one, which might be of use:
Switching to rollers - and why you should try too - Training - TrainerRoad