at: Update time format - fixes #4192 (#4202)

pages/linux/at.md

@@ -4,15 +4,15 @@
 
 - Open an `at` prompt to create a new set of scheduled commands, press `Ctrl + D` to save and exit:
 
-`at {{hh:mm:ss}}`
+`at {{hh:mm}}`
 
 - Execute the commands and email the result using a local mailing program such as sendmail:
 
-`at {{hh:mm:ss}} -m`
+`at {{hh:mm}} -m`
 
 - Execute a script at the given time:
 
-`at {{hh:mm:ss}} -f {{path/to/file}}`
+`at {{hh:mm}} -f {{path/to/file}}`
 
 - Display a system notification at 11pm on February 18th: