How long post SHTF before a city is safe to re enter?

[Hrusai]

if its a supplies driven scenario you are better off scavenging from houses and the outskirts of population centres, ANYTHING you need will be in the countryside, almost everyone has sheds full of tools, farmers have stockpiles of supplies, if you need medicine, raid a nursing home, no joke they got lots of medicines in there, and low security, and anyone in there will be long gone by the time you get there

end of the day only reason to go into a city is to rescue someone taken by someone else, and if that happens chances are they're family and you'd be going on your own, and thus moving quickly and quietly anyway.

if anyone can think of some mystical item only found in cities please share so i can stock up