Cron Expression: Every Weekday at 9am

Field by field:

• Getting the time zone right matters most here. A UTC schedule sends your 9am email at the wrong local time for half the year once daylight saving kicks in.
• Runs once a day, so it fits Vercel Hobby, with up to 59 minutes of jitter.

Checked against each platform's rules, assuming UTC:

• Every Minute* * * * *
• Every 2 Minutes*/2 * * * *
• Every 5 Minutes*/5 * * * *
• Every 10 Minutes*/10 * * * *
• Every 15 Minutes*/15 * * * *
• Every 30 Minutes*/30 * * * *
• Every Hour0 * * * *
• Every 2 Hours0 */2 * * *
• Every 3 Hours0 */3 * * *
• Every 6 Hours0 */6 * * *
• Every 12 Hours0 */12 * * *
• Twice a Day0 9,21 * * *
• Every Day at Midnight0 0 * * *
• Every Day at 9am0 9 * * *
• Every Day at Noon0 12 * * *
• Every Weekday0 0 * * 1-5
• Every Weekend0 0 * * 6,0
• Every Monday0 0 * * 1
• Every Friday at 5pm0 17 * * 5
• Every Sunday at Midnight0 0 * * 0
• Every Week0 0 * * 0
• Every 15th of the Month0 0 15 * *
• First Day of the Month0 0 1 * *
• Last Day of the Month0 0 28-31 * *
• Every Month0 0 1 * *
• Every Quarter0 0 1 1,4,7,10 *
• Every Year0 0 1 1 *
• Every Hour During Business Hours0 9-17 * * 1-5
• Every 30 Minutes During Business Hours*/30 9-17 * * 1-5

Or build your own in the cron expression builder.