How create a crontab on mac?

I've tried [crontab -e](https://unix.stackexchange.com/a/212705/302720) which takes me to what appears to be an empty file opened with vim. I make no changes and simply press esc, :, w, then q to save and exit. But when I try crontab -l I see:

crontab -l
crontab: no crontab for st

I tried the same thing [as root](https://superuser.com/a/540693/928461) but I get the same outcome

MacBook-Pro:~ root# crontab -u st -e
crontab: no crontab for st - using an empty one
-- I save an exit vim as above --

crontab: no changes made to crontab
MacBook-Pro:~ root# crontab -u st -l
crontab: no crontab for st