Right - the main reason for scheduling these events in the future is to ensure there is a sufficient round-trip-time from sensor reading to PWM update.
I’m sure it is possible, but I don’t think it would be straight-forward. The challenge is ensuring the safety checks remain in place (in particular the maximum duration checks). For what it is worth, I view the heater PWM pins as “critical to be set correctly” and I’d be a little leery of the mcu processing simple “turn yourself on” commands without a more explicit context (such as a timestamp). I do understand your concern with the timing of the feedback loop though.
Cheers,
-Kevin