Why you can't use a range here
Cron's week runs 0 (Sunday) to 6 (Saturday), so the weekend sits at both ends. A range like 6-0 is invalid — ranges must ascend. The comma list 0,6 is the correct form. You may also see 6,7 used, since 7 is an alternative encoding for Sunday.
Frequently asked questions
What is the cron expression for Saturday and Sunday?
0 9 * * 0,6. Use a comma list because the weekend days are not adjacent in cron's 0–6 numbering.
Related cron expressions
Browse the full cron expression reference, or build your own expression from scratch.