The custom code condition 'check-in is in ... days ' uses units of days and not hours.

This means that a condition of 'check-in is in less than 2 days' is met only when the event happened 1 day or less prior to check-in. We do not treat it as less than 48 hours. If the check-in was on Nov 3rd 1pm, the custom code would not be populated if the message is sent anytime from Nov 1st and earlier. It would not be populated if sent on Nov 1st 5pm, which is technically less than 48 hours from the check-in. For the custom code to be sent on Nov 1st, you would need the condition 'check-in is in exactly ... days'.