"Alexa, start stop watch" or "Alexa, open stop watch".
The elapsed time is shown in hours, minutes and seconds.
Additionaly to the Alexa voice the Skill will show an historic picture of an old time-measurement device in the Alexa App, your Alexa Show or your Alexa Spot.
"Alexa, tell stop watch to pause." Will pause the stop watch. You can tell the stop watch to continue to run by saying: "Alexa, start stop watch."
"Alexa, ask stop watch for current measurement" Will tell you the elapsed time.
Happy time keeping and if you find the skill useful, leave a review here.
P.S. It is important to say: "Alexa, start stop watch." without an article; if you say "Alexa, start a stop watch." it will NOT work.