This is not ture, a level 5 cooking plant needs 126 seconds of licences per coal it makes (this one is easy to calculte: 3,5 licences to keep the chain running devided by 5 coal every 3 minutes times 180 seconds = 126 seconds). The level 3 chain will need around 210 seconds of licences per coal.
While a level 1 coal mine will need around 158 seconds of licences per coal. This one is very difficult to calculate, so i just used the data from http://www.siedlertools.de/wiki/Kohl..._K%C3%B6hlerei
The level 2 coal mine will need around 173 seconds of licences per coal.
These numbers for the coal mine assume the mine is up 100% of the time (no build time and no geologist time) and that it is not torn down when low.
If you assume you tear every coal mine down when it has 1 or 2 coal left, then it'll come down to around 142 seconds of licences per coal for both level 1 and level 2 coal mines.
All the calculations above ignore the travel times.