See model definition: https://developers.formstack.com/v2.0/docs/portals#section-portalform

Control deadline reminder

pass in earlyReminderHours or earlyReminderDays under deadline model. (depends on your chosen deadline type - see definition at https://developers.formstack.com/v2.0/docs/portals#section-deadlines)

For example, for PortalFormDeadlineWeekly , pass in the following object to set up weekly deadline every Friday at 8pm, with a reminder 2 hours before deadline:

"deadline": {
  "frequency": "weekly",
  "dueDay": "Fri",
  "dueTime": "20:00:00",
  "earlyReminderHours": 2
}

To disable reminders, pass in earlyReminderHours and earlyReminderDays as null

On success - returns newly added portal form representation.