The Robinson to St Mirren appointment was largely met with positivity. He had a poor start and there was (bizarrely if not surprisingly) restlessness within a matter of weeks. The key difference there is that he was starting from the club being in a reasonably good position (relative to previous seasons).
There is an argument that your new manager will be cut a fair amount of slack as things are unlikely to get much worse. That, however, hinges on managed expectations. I'm already seeing posts about a cup win and top four finish within his first season. Perhaps not entirely unreasonable given the size of the club, budget available, etc, but I recall McInnes doing pretty well but it was never quite good enough for a substantial proportion of the Aberdeen support.
I would have thought that a solid top 6 finish and a tilt at Europe in his first season wouldn't be a failure, no?