Reminder emails to respond to a prompt are set to go out every other day, only on weekdays.
How to disable the reminders:
1. Select the prompt from the dashboard.
2. Click "Recipients" from the left-pane menu of the prompt editor.
3. Under In Progress section, from the list of recipients, look for the contact you want to disable the reminder emails for.
4. Click the "X" button next to the reminder schedule for the recipient.
5. Then click "Yes, Cancel Reminders" to confirm.