I am charged Hobbs time, I log Hobbs time. It is started by oil pressure from what I remember. The field I fly at is uncontrolled, and procedure is generally start up, post start up checks, obtain airfield information and then taxi to hold to do power checks (after letting everything warm up). So I might be "stealing" a couple of minutes every flight, but considering I log decimals, this is more often than not, not going to make a difference to log book time.
On a side note, whilst I can't see the "intention of flight" bit anymore, I have copied this from GtE's post:
"in the case of a piloted flying machine, from the moment when, after the
embarkation of its crew for the purpose of taking off, it first moves under its
own power, until the moment when it next comes to rest after landing"
Is "for the purpose of taking off" not essentially the same as "for the intention of flight"?