Countdown Timer from Joda.time to Java.time (Openhab 3.x)

In OH 2.5 long running rules run risk of using up all the execution threads making it so none of your rules can run. That’s not a pregnant in oh 3 any more. (OH 1.x and OH 2.x Rules DSL only] Why have my Rules stopped running? Why Thread::sleep is a bad idea

I’m rebuilding from scratch so I don’t know the best way to migrate.