Is it possible to use feed time for calculations with pulsecounter?

Hi, I have a gas meter and a KWh meter that send only a counter value ( i.e.  42 43 44 45 46 ...etc) every time the counter is incremented. I would like to convert those pulses to watts . Unfortunately the Arduino cannot send also a time information (since it is in low power mode and millis() does not work).

I thought also that I could send the counter value every 15 min, but then if a packet is loss I wouldn't have reliable watt hours.

I think that Emoncms has the time information about when the data has been received. I could do

(counter(1) - counter(0))*(time(1) - time(0)) and have the watt value 

is it possible to do such a thing?