Hi Ben,
You might try created a systemd service for it instead.
I think more about this tomorrow, when my brain has rebooted, but I
think if I did it that way, all the different users would be using the
same polling period coded into the common service file.
My original re.local file had a string of commands like:
su tim -c "/usr/bin/fetchmail -d 900"
su adam -c "/usr/bin/fetchmail -d 1200"
su eve -c "/usr/bin/fetchmail -d 1500"
Each with a different delay, so that traffic was staggered.