Adjusting ignition timing on Carbureature cars is very simple, you just need to loose and rotate the distributor but since Altis is EFI and probabily with a Timing Advance Processor installed, so I really can't comment on it.
You should consult the shop where got installed your CNG kit or try to locate ENERCON workshop in your area. They tune up your car by examining the the CO emission from exhaust, thus optimizing the engine performance.
BTW: In my life, I haven't seen a mechanic with a Timing Gun to check ignition timing, even those who install the Timing Advance Processors in EFI cars. (bad ignition timing can ruin your engine's performance)
Another cause for starting on 2nd or 3rd crank is out of range adjustment of CNG. If you are getting good mileage, may be your CNG setting has been at low end. In this case, pick becomes poor, however.