The cron day of week field: 0 to 7 with Sunday at both ends

The week starts on Sunday in this field, which is the convention inherited from the original Unix cron and is not negotiable. Monday is 1, Friday is 5 and Saturday is 6, so the working week is the range 1-5 and the weekend is the list 0,6.

Sunday appears at both ends of the range. The field accepts 7 as well as 0 and folds 7 down to 0 before matching, which exists so that expressions written for schedulers that number Monday to Sunday as 1 to 7 still behave sensibly. The practical consequence is that 0,7 is one day, not two, and that 6-7 is a valid way to write the weekend.

Names are accepted and are usually the better choice. MON-FRI says what it means without requiring the reader to remember where the week starts, and the parser treats it identically to 1-5. There is one gap: the parser screens every field for the Quartz characters L, W, # and ? before it looks up names, so a field containing WED is rejected as though it held a W. Write Wednesday as 3 here.

The important thing about this field is what happens when you restrict it alongside the day of month field. Cron then matches a date if either field matches, so an expression that looks like a narrowing is actually a widening. That rule has its own page, and it is the single most consequential piece of cron behaviour to know.