AWS Serverless Service to trigger an event when something doesn't happen

Question

I'd like to use some sort of AWS serverless technology to trigger an event when a clickstream stops receiving clicks. Imagine a website visitor clicking around a site. Within our current solution each click is being sent over http to an AWS API Gateway which uses a Lambda function to push the value into DynamoDB. I'd like to trigger an event when the clickstream stops; say, 5 minutes after the last click was received (per visitor). The 'lack' of further clicks indicates that the visit has concluded, at which point I'd like to take some further action

I'm keen to maintain our AWS serverless approach. Do AWS offer an 'out-of-the-box' service which would deliver this capability? I need the resolution to be a few seconds, not minutes or days. Thanks.

• GHP: Seems like a separate task on an interval (every few seconds) would do the job of checking the data for activities which occurred within the last XXX seconds/minutes, but whom don't have their newest entry being less than XYY seconds/minutes from the current time.
• Journeyman: @Graham - thanks for what I'm sure would be a perfectly fine solution. But what I'm really wondering is whether AWS have some sort of native service which could be configured to deliver this functionality without having to roll-my-own solution. e.g. AWS DynamoDB tables support triggers on insert - very useful for calling lambda functions. There is also an 'evaporation' capability where records auto-expire, but the time resolution is hours not seconds. I guess I'm looking for some sort of configurable event-bus functionality that has a flexible config that would support this sort of thing.