Why not just create a macro that turns the pump on, delays for 5 seconds, and turns it off?
You could trigger it with a timer as needed.
Yep! That is the solution. But because it is a pump.... maybe a safety of some sort should also be used. I have worked pretty hard to have a clean setup. But still from time to time a light doesn't go off, or I miss a voice message due to a signal collision. Particularly if the user is also using sensors and/or macros that could generate line signals at a home that isn't monitored closely... safety should be considered.
If this is a water pump that failed to shut off.... running continuously for 7 days until it cycled again... that could be pricey. Even assuming the pump doesn't fail before the week ends.... or the well doesn't run dry. Of course... just being "powered" doesn't mean the "normal pump safeties" wouldn't still apply. For a well-water pump to run... low tank pressure would be required.
But I would at least add a second delay.... and a second off. So say the pump comes ON at noon on Mondays. Delays 5 sec and then turns OFF. Delays one minute, then turns OFF again.