Yep it is also called advancer, It's proper name is Sequential Timing Advance Processor. It advance the timing for CNG, you have to set up car perfectly on Petrol first, proper Timing Proper RPM, etc.
Then you add the advancer, and adjust it's timing (advancer) on CNG. After that you can adjust the CNG Nut on main line going to adjust CNG's air fuel ratio, then adjust the rpm using the cng kit nut.