Last night I setup RDNS for /48 netblock... How long will it take before those 2001:470:c14c::1 (for example) begins to resolve?
That would depend on the TTL set for the zone, assuming of course HE knows about your nameserevrs being authoritative for said zone, etc etc etc.
Looks like it's on ns1.he.net, and ns5.he.net. Just needs to propagate to the other 3.
Which it finished about 15 minutes after I checked.