It's the function variable for the multiplication operation.
https://docs.python.org/3/library/operator.html#operator.mul

I did it just like this.

You construct a timedelta object by providing the given parameters (hours, minutes, seconds) then you can convert it to any time unit by // dividing it with an other timedelta object which you instantiate with the correct unit (in this case 1 milliseconds).

https://docs.python.org/3/library/datetime.html#datetime.timedelta.total_seconds

It shows the built in seconds converter and lots of other useful method.