Charlie,

If 1/2 a second is anywhere near actual, you probably didn't do any damage.

I would use the garden hose "Ear Muffs" to get water to the engine and start
it up with the COVER REMOVED.

Watch the weep hole for the "tell-tale" stream of water to confirm that the
pump is working. This is not a 100% guarantee but at least an encouraging
sign. If you have real high water pressure and a tight fitting ear-muff you
could force water past a bad impeller.

So.... if in fact you do see the tell-tale stream let the engine run for a
period and feel around on the engines water jacket for hot spots, it should
get no hotter than you can comfortably stand. Use your fingers cautiously
at first so if it is real hot you don't scorch a finger, or a inferred
digital thermometer. If there is even the 1st hint of paint becoming
overheated and smelling, or the engine is warmer than you think it should
be, turn off the engine immediately and replace Impeller and Pump Housing.

I would next make a special trip to the lake on the least busy day and back
the boat into the lake enough to cover the cavitation plate a couple of
inches, being certain that the prop will not hit the boat ramp and start the
engine. Leave boat on trailer.

Start the engine, with cover off, watch for telltale stream and again feel
and check around the engine power head block for hot spots.

If it passes these test and does not at any time activate the over-temp
warning signal, you probably lucked out. With the cover still off make an
actual boat ride test at idle speeds and if still no overheating gradually
increase speeds in modest steps checking temp constantly.

If all of this passes, thing are most likely OK.

I indicated a quiet day on the lake, and I would not take the whole
neighborhood for a day of boating, this it a TEST day only.

For the first few times of actual boating be extra alert for an over heating
problem and do not turn the boat over to someone else to operate unless you
are in the boat being alert for the overheat risk.

Don Dando