Use case: User creates meeting appointment and should be notified in 24 hours/1 hour/5 minutes before appointment. Current implemetation:

1. When appointment is created, it is saved in DynamoDB with ttl (appointment time - 24 hours)
2. When ttl is expired, DynamoDB removes this item.
3. There is a lambda that listens to DynamoDB stream event and is triggered by previous action. There are 3 additional boolean flags in item: 24hours, 1hour, 5minutes. When item is removed before 24 hours, this lambda sets 24hours flag to true (in order to know in the next step that push notification before 24 hours already has been sent) and saves it again with new ttl (appointment time - 1 hour), push notification is sent.
4. Same as in 2 and 3: ttl expired, lambda sets 1hour flag to true and sets new ttl (appointment time - 5 min) and saves item again, push notification is sent.
5. Again: ttl expired, push notification is sent.

Concern: DynamoDB does not guarantee that item will be removed exactly when ttl expired.

Is there any another solutions: more efficient than mine?

Current stack: AWS/Serverless Framework/NodeJS.