To keep forms with Identity Checkpoint enabled from timing out for users, it is recommended that you keep the first step of the form simple since it must be submitted within ten (10) minutes of when the user first lands on the form page.
If you have a long form with lots of text area fields, you could add a Save button (in addition to the Next button) with some rich text advising users to save their work as they go.
You could also add steps so that fewer fields are on each step which should enable the user to complete each step a bit faster.
NOTE: The ten minute time out is in place to prevent data mining of the user's information.