Create cron job using AWS lambda

Hi guys,
I'd like to implement a mobile app (using Xamarin) that inserts and modifies "events" on a calendar (table on DynamoDB). So I found a post which tells how launch a lambda function inserting rows in a table (using AWS Streams). Ok, at the moment, my app can write in that table (timestamp and duration) and a lambda starts.

Now, I need that the lambda function creates the cron job which starts at "timestamp" time for a "duration" seconds. In particular, that cron should send a mqtt message to an IoT device..

Thanks a lot

Giaco