What's the name of a timeout relay which won't re-trigger if it times out?
It sounds as if all that you need to do is add a "Delay On" timer to your existing relay.

You will want to purchase a 2-pole timer relay with delay-on function. The reset button is normally-closed and is in series with the time-delay relay's coil.  Pressing the reset button will cause the relay to turn OFF after it has latched ON.

One pole of the relay is used to latch-on the time-delay relay after it has triggered. The other pole disables the pump. 

Ask if the above isn't clear and I'll add a schematic when I'm in front of my computer.