Similar to T202576:
Give local wiki admins (or editinterface permission holders) the ability to set the default block expiration on Special:Block.
We can also consider to make this more sophisticated, by changing the block length based on other parameters (username, block reason, etc.)
This is already an option. The default for all blocks is set at MediaWiki:ipb-default-expiry. T219126: Create a MediaWiki:ipb-default-expiry-anon for setting default anon. block durations separates this to allow a different default for IP blocks. I'm not sure when the customization was originally added, but the earliest reference was @daniel's commit https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/20715/ - see https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/20715/1/includes/specials/SpecialBlock.php at line 147