provided by Star2Billing S.L.

Hey sometimes people complain that they got billed without being connected. If you do record_call = Yes, then you can check the call and verify, but you eat up disk space. It would be nice to record the first 15 or 30 seconds of a call only so that if someone disputes it, you could pull the recording up and know for sure. Anyone know how to do this ??

Reading the documentation for MixMonitor(), which A2B uses to record the calls, shows that it doesn't have a timeout parameter so it's not simple to do what you want with A2B v1.3.x.
That page also indicates that MixMonitor exposes an Asterisk CLI/AMI interface capable of stopping recording, so what you want would be fairly easy if there were already some piece of code monitoring the active channels on a regular basis. This is where asiby steps into the limelight, as he's been working on such a piece of code for a while now. Perhaps you might see your feature request in a future version of A2B one day.