For the sake of an Answer, copying a Comment:
Done. More countries welcome. – chx Jan 22 at 18:18
I think what was "Done" may have been the following being added to the visas tag wiki:
Some countries where a valid visitor visa is necessary only to enter
and your time to stay is set at the border:
Some countries where you need to leave by the time your visa expires:
We do have a tag visa-expiration (as well as visa-extensions, amongst many others concerning to visas) for which the Usage guide is, at present:
Tag for questions such as "Does my visa expire at midnight of the last day?" or "Can I leave the Schengen on the 91st day?".
(no tag wiki for it at present) and there is the following in the tag wiki for visas:
Visas indicate that the holders thereof may present themselves at a border and request entry into the issuing country. Visas may have both a duration of validity and a visit time limitation.
Duration of validity here means the period over which the visa itself is valid. Thereafter the visa, whether or not by then presented, expires. In some countries, you need a valid visa to enter the country, in others you need a valid visa to be in the country. See a partial list below.
Visit time limitation, often 15, 30 or 90 days, here means the maximum period of time allowed in country if entry is granted. The person responsible (border control) for allowing or declining entry may decide upon a visit time duration that is less than the maximum available for the relevant visa, or decline entry altogether.
The latter (visit time limitation) is a matter of “What is the longest I may stay if I am permitted entry?”. The former (duration of validity) is a matter of “When is the cut-off for use it or lose it?” For the latter it may be worth bearing in mind that, at least in theory, the visa application process is to permit countries to ban entry to people they consider undesirable. Therefore a time limit is necessary to allow for a change in circumstances, regarding the deemed desirability of a visit by a specific individual, that my take place long after a visa was issued.
“In theory” because in practice visas are essentially just a means to tax prospective visitors, often tit-for-tat in response to the charges imposed by the home country of the would-be visitor on visitors from the country issuing the visa.