More tasks should eventually be interruptible & resumable, but few are currently. It can be noted that those that can be interrupted will automatically pause the task when you're too tired (due to fatigue and/or needing to sleep) while those that can not will continue the task until it's finished, at which time your character immediately falls asleep if too exhausted (which is annoying when the extremely long and heavy tanning task also leaves the character extremely hungry, losing further nutrition levels during the sleep).
Some tasks will refuse to start at all if they would take too long (typically involving tools unsuitable for the task, such as e.g. stone axes), and some, which are borderline cases, will start only if the duration roll was favorable.