id say use hubcentrics as soon as the wheel is no longer resting on the hub!!
the bolts arn't designed to take the weight of the car!
personally id poo myself everyime i drove if i had over 10mm without hubcentrics!
also,
hubcentrics is just the name thats given to spacers that fit the bore of the wheel, and have an identical bore on the spacer, so that the weight of the car isnt on the bolts.
its not just the name of bolt on spacers, though they are also hubcentric! you can get hubcentrics that just use longer bolts!!
hope this helps.