Standard agressive response. You're displaying that famous lack of self-awareness again. It's not a good trait. And you admitted that yourself which makes it worse.
But to answer your question - let me put it this way: If you were drafted into a new job (let's say any field of work for simplicity) in which the team that you were hired to managed were performing badly, then how long would it be until you thought it was fair for others to judge your performance?
Allardyce is doing what Allardyce does, shit football with mediocre results. You could give him another 12 months but you’re probably only get what he’s been doing for the past few decades, shit football with mediocre results.
If we wanted any different we should have hired someone else. Same as @Bluedylan
’s hypothetical employer.