I havent heard of timing affecting starting so much as giving pinking (rattling sound in engine on acceleration) which is also affected by the fuel octane rating. Most people set their timing to the book and then, if theres pinking with the fuel they want to use, back off the setting until it stops (definition of this is the rattling ceases on reaching 2000rpm when under full acceleration in 4th gear on the flat). Of course everything else has to be correct such as mixture, distributor condition etc...