Actually, it would need the same time as someone who's paying attention. On top of that, it can't pre-emptively Cure, so you're always in a pretty bad place if you're fighting something that can take you down fast.
Personally, I'm a better WHM than my PLbot, the only exception to that (from lack of practice recently), is my Haste timing, sometimes I cast too early, sometimes I only cast when it wears off, but my status removal, cures, cureskins, bar-spells, are all much more efficient.
A PLbot will give a bad WHM an advantage in the sense that it'll cure everyone (almost flawlessly), it'll buff everyone and it'll Raise people. A good WHM (hell, even a decent WHM) will be able to do a better job theirselves.
Bots are
slower than people, there's many times I've swapped back to my WHM's screen to Cure/Buff myself before/after something goes wrong.