Which Opentime subscription is applied to which city?

The number of active Opentime subscriptions controls the number of bases available to be configured on the Opentime Settings page.

Therefore, no particular Opentime subscription is linked to a particular base. If you want to keep a particular base, then ensure that base is at the top of the list on the Opentime Settings page.

Note that the base list will shorten only when the subscription expires. A cancelled subscription will run until the end of the three month period. See (I cancelled my subscription but I still get Open Time Alerts!?)