Trigger an URL at a specific time (AWS)

Any ideas on how to reliably trigger an URL (web service) at a specific time? With the precision in seconds? For example, the script will be set so that it will be able to trigger a web service at 2015-05-27 12:34:55. In my scenario, the user will be able to select at what time, down to seconds a trade should execute. The web service must be then triggered at a specific time

• AWS Lambda is not able to run at specific times.
• Cron jobs won't work as it does not run every second
• An SQS might work but coding it up to be reliable could be hard.

Thanks!