For those that want to know,
All my dash lights go out in 6 seconds or less upon a cold start after an
overnight period.  The coolant blinking light goes out in 6 seconds, timed
with my watch.
If your takes longer, you might have a problem.

I disconnect the sensor once in a while to make sure the circuit is
functioning correctly.  I would advise any one to check theirs.  Disconnect
with the engine running to make sure the light starts flashing.

Robert