Feature request: schedule future snapshots

[MCFurry]

In some occasions it would be really useful to trigger a snapshot on special events (i.e. collisions or diagnostics) but then also record a little bit of the future.

Proposed would be to call the service with a stop_time in the future and the snapshot service waits for this stop_time to have passed?

I.e. in python like so:
TriggerSnapshotRequest(filename='snapshot', stop_time=rospy.Time.now() + rospy.Duration(5.0))