What is the easiest way to “detach/daemonize” a Bash script?

What I am trying to do is write a Bash script that sleeps for a set amount of time before using the mac say command to speak some text.

I'd like to be able to run the command and then close the terminal so it will still speak at the set time. I've looked into nohup, detach, launchd, and putting the process in the background, but all of these solutions still result in the process being terminated once the terminal is closed. Should I somehow make some sort of zombie child process to do this? What is the best solution? Thank you

# Simple Example of main code
sleep 10;
say hello;
exit;