Cases: auto-calculate expiry date based on issue date + 'indefinite' option

Please can you add an “Indefinite” option to Cases. Referrals to Specialists are either valid for a year (“standard”) or indefinitely; Medipass claims reject if we forget to manually change the referral period from standard to indefinite.

It would be great to have a box to check that would automatically calculate an expiry date of 12 months after the issue date too.