Devices manufacturers such as Eufy (and I highly believe all of the major ones) already work on the new firmware update to support Matter, for very long time ever since they (the group) announced the plan. Nobody could possible release firmware update even before the standard released. But we could possibly see the first ever Matter supporting firmware update in the coming days or weeks. But most of them should take no more than 4 months or so.

This is NOT like a USB4.0 standard where a bunch of people pave the road and people follow at will. Instead, it's basically the players making a plan while practicing according to the plan. Very similar to how F1 make/change their rules: before the change of rule made it to the public, all teams have already been working on it.