I don't think the timing can be criticised.
In hindsight, it might turn out that he should've gone earlier. I was one of the ones who'd have been happy if he'd been sacked pre-season.
That said, he'd earned the right to start this season and the club gave it as long as they could. They'd made a commitment that ended up being the wrong one. Can't blame them for leaving iong as was possible. It didn't work but it might have.