I am impressed at the amount of downvotes. The US had crossed several thresholds now which would've (and should've) caused Civil wars a while ago or in other countries.
Downvoting the post above confirms it has not yet been understood where the US now stands.
Depends on the location I guess. Here it's mostly done and since it doesn't really take any effort I would agree a look behind and holding the door is something everyone should do.
Germany: 24 would be the legal lower limit, but it's almost always 30 days (+ bank holidays). If you're disabled add 5 more.