When I do crontab -e, are the changes applied immediately when I save the file, or do I have to exit vim for it to be applied?
Are changes in crontab applied when the file is saved, or when the editor is closed?
cron
It waits until you exit the editor. From the manpage:The  -e  option is used to edit the current crontab using the editor specified by the VISUAL or EDITOR environment variables.  After you exit from the editor, the modified crontab will be installed automatically.You can also tell by just watching stdout; it waits until you exit the editor and then outputs:crontab: installing new crontab