Subscribe with your calendar
The feeds list upcoming and active offers. Ended offers drop out of the feed and stay on the week and game pages. No login and no payment.
Times in the feed are UTC. Your calendar app shows them in your local zone. If the store did not list an exact end, that offer is left out of the feed rather than given a made-up clock time. A date with no clock time becomes an all-day event. Reminders (24 hours and 1 hour before the end) are added only when the end is an exact time.
Google Calendar
Google Calendar: open Other calendars → From URL, and paste the https link.
Apple Calendar
Apple Calendar: use the webcal link, or File → New Calendar Subscription.
Outlook
Outlook: Add calendar → Subscribe from web, and paste the https or webcal link.