Erm let's go with (semi)educated guess.... It's difficult to turn the tide when fans and press feel so strongly so quickly about a manager and his competence/ability.
Sometimes a player just doesn't fit a team and from time to time it happens with managers also..... Imo it's not even his fault ( so far ), he's been screwed from above in the window ( until the last minute if we're being kind ) and still didn't get a striker. His performance was going to be under the microscope instantly from some due to the popularity of our previous manager and where we finished last season and anything less the perfection was going to draw unfair (some would say ) comparison. I think he deserves 10 games from the close of the window, but if thinks don't improve almost instantly I'm not sure he'll see that
Next couple of games are huge for him imo
Regarding how long a manager should get, I'd typically say quite a long time. Couple of windows at least. I don't like the constant changing of managers in modern football. However, it obviously has to allow for the state of things. When you're dropping like a stone and the manager has clearly lost control then they have to go. No one would argue that Shota, Slutsky, Parkinson or Molby should've had more time even though none of them got very long at all. Realistically we couldn't afford to let them have more time. In all of those cases, sacking them turned things around quite quickly. Walter isn't quite at that stage yet where it's unavoidable but I think there are strong signs of it already.
If and when we do sack him, it'll be a bad look having sacked four managers in less than three years. But in that scenario, sacking Walter (and Shota previously) isn't the bad part. It's the McCann and Rosenior ones that were avoidable.