Yes program 2 waits until program one is closed again, so you have to put a & at the end
https://stackoverflow.com/questions/3004811/how-do-you-run-multiple-programs-in-parallel-from-a-bash-script
#!/bin/bash
# DietPi-Autostart custom script
# Location: /var/lib/dietpi/dietpi-autostart/custom.sh
sudo nice -n 19 Program 1 &
sleep 5
sudo nice -n 10 Program 2 &
exit 0
The & puts the process in the background and continues with the next line