ThunderSkye,
It appears that the answer is in fact contained within the AIM. (thanks, Jetavia) It looks like when you are flying the hold by reference to DME or RNAV, as in a defined leg-length hold, it is the outbound leg that is measured and defines the point where the inbound turn is commenced. Only on timed holds is the length (elapsed time) of the outbound leg adjusted so as to cause the inbound leg to last the appropriate length of time.
Thanks for sharing this one, Thunder. Since I have a trip to Chi-town later this week, it probably means I'll get assigned a hold too! At least I've now had a refresher on what to do when I get it. Thanks, buddy!
Best regards,
Westhawk