To customize the frequency and reminder schedule of your Check-Ins go to My Team's Check-Ins --> Customize Check-Ins.
Here you can adjust how often your team will submit Check-Ins and the day you'd like them to be reminded. If you decide to request Check-Ins bi-weekly or monthly then the reminder is only sent on a week where a Check-In is due.
Don't forget to save changes!
Note: You can customize how often your team is reminded to Check-In, but Check-Ins always begin on a Monday and end on Sunday. You can also customize when your team will receive their email or Slack reminder to check-in.