I can see the logic in delaying an announcement until a) season end and b) Brands appointment but after those, there is really no need to delay it any longer if indeed it's happening.
The only other reason to delay is if they want to announce a successor as soon as possible afterwards, and are waiting on a yes from someone. Even then I don't see any benefit to that although I imagine Allardyce would gripe about the club going behind his back and we would probably get criticism from the LMA and media, but that's hardly unexpected.
Surely Brands will be announced next week and Allardyce if he is going, shortly after. I just hope they have clarity on a successor, and if an agreement isn't already in place, then the process is at least narrowed down to 2 or 3 available and viable candidates. We should be looking to have a new manager in place without delay, but no later than the end of the month.