Where and when to check the expiration date and cancellation date of the subscription in the app ?

Good afternoon, I have a question about InAppPurchases Auto-Renewable Subscription.
Paid subscriptions can be cancelled at any time.

Where and when to check the expiration date (and possible cancellation date) inside the application ?
Do I need to call restoreCompletedTransactions every time in didFinishLauchingWithOptions to get the current date ?

Where and when to check the expiration date and cancellation date of the subscription in the app ?
 
 
Q