Exactly as the title says, changing the number of days it is delayed doesn't do anything and the hordes only spawn every ten days

Which version?
Did you change the config after creating the world?

1.19.2
After, does it only affect new worlds?

It should affect current worlds as well, but due to how the day calculation works it has to catch up first, when the next horde passes it should update to the new value, or you can use /hordes reset