Design a generic timer service to cater to timer requirements from different teams in your company.

The teams would use your service to be notified that a specified time duration has elapsed. Each team could be handling thousands or millions of transactions of different nature, and the timer service could be used after each such transaction. So design a service which can scale accordingly.

For instance:
Team A: notify that a minute has elapsed after a transaction.
Team B: notify that an hour has passed after a failed transaction, for retrying it.