With maintenance windows you can schedule planned maintenance for whatever you are monitoring in order to prevent your checks from running at specific times. Maintenance windows have their own resource: 
resource "checkly_maintenance_windows" "maintenance-monthly" {
  name            = "Monthly maintenance"       // The name of the maintenance window
  starts_at       = "2022-08-24T00:00:00.000Z"  // The start date of the maintenance window
  ends_at         = "2022-08-25T00:00:00.000Z"  // The end date of the maintenance window
  repeat_unit     = "MONTH"                     // The repeat strategy for the maintenance window
  tags = [                                      // The tags of the checks and groups maintenance window should apply to
    "auto"
  ]
}
You can see all the configuration options for maintenance windows, as well as more examples, on the official Terraform registry documentation page.