Power output of ignition coil - 2.0
$$ E = P \times t $$
Energy is power by time.

If your ignition coil outputs the same energy regardless of the duration then yes, the average power must reduce if you extend the time.

The energy in your example is given by \$ E = Pt = 60k \times 1m = 60 \ \text J \$.


  What is the formula to convert watts-miliseconds to watts-seconds or watts-hours?


\$ 1 \ \text {Wh} = 60 \times 60 \ \text {Ws} = 3600 \ \text {Ws} = 3.6 \ \text {kWs} \$.

Converting to watt-milliseconds is likely to cause confusion as the abbreviation will be kmWs or similar.