Jobs added to a live folder can start instantly

Jobs shall be able to be started instantly when they are added to a live folder.

Implementation:
With <at> there should be the possibilty of using the attribute at="now" to start jobs instantly.
In addition at the attribute "at" the values "now + HH:MM[:SS]" and "now + seconds" should be possible to use, too.

Current Situation
Until now it is only possible to choose date and time:

<job>
  <run_time>
    <at at="yyyy-mm-dd hh:mm[:ss]" />
  </run_time>
</job>

Desired Behavior
New possibilities for runtimes:

<job>
  <run_time>
    <at at="now" />
    <at at="now + HH:MM[:SS]" />
    <at at="now + seconds" />
  </run_time>
</job>