Upgrades from Ubuntu 24.04 LTS to Ubuntu 26.04 LTS are offered after the release of Ubuntu 26.04.1; that’s scheduled for [late] August, so it’s not quite six months (six months away is Ubuntu 26.10).
Ubuntu 25.10 reaches EOL in three months; so the upgrade from it has to open before that date, it’s expected, as I stated in days or weeks, or as Ian suggested a couple of weeks. It’ll happen before it reaches EOL at minimum.
The upgrade from 24.04 to 26.04 is a large step; upgrading through four releases, or a full two year development cycle; where the upgrade from 25.10 (to 26.04) is a somewhat tiny step (in comparison) that’s why it’s always much much sooner; after all many of the upgrades happened in prior cycles (24.10, 25.04 & 25.10 - so its only the last portion).