If you used the latest version of Mainsail(v7.0) skip this next command.

git clone https://github.com/mainsail-crew/moonrak...

Regardless if you used the latest version or not run

bash ~/moonraker-timelapse/install.sh

Make sure printer.cfg calls the timelapse config

[include timelapse.cfg]

Make sure the [timelapse] section is uncommented in moonraker.conf