To expand a bit on what Kristen said: Except for the higher profile races where riders often arrive at the vet check at speed, the actual time to reach criteria at vet checks from "trail speed" is currently unknown to the timers & vets. Having worked many a PR area, it is rare for riders to arrive at the in timer NOT already off their horse and walking. The horses begin "recovering" as soon as they are brought down to a walk. They may be "recovering" for 5-10 minute before they even get to the in timer, especially if there is water close to camp and they've stopped to drink and sponge. This doesn't happen at a 50 mile finish line. People ride to the finish, usually at least trotting, then get off and do what they want to do before getting a pulse. If you want to time the finish line like a vet check, then make pulse criteria the "finish line" just like LD. Not MY idea, but just think of how many safety issues THAT would solve.
I've read several suggestions that rides with vet checks out of camp could allow the ride manager to "adjust" the 30 minute rule to give them time to reach the vets. The biggest problem is that would indeed give those horses more time to recover, even though they are walking, they would/should be recovering as well.
I also do not believe "crash cooling" is in the best interest of the horse.
On balance I think the 60 minutes at the finish has served the sport well. If anything is changed, perhaps a 15 minute pulse (or as soon as arriving from the finish if distant) should be required of all finishing horses not just top ten. Just a pulse recorded by the timer (not CRI) wouldn't require a vet or take a lot of time, but it would identify horses still high for closer monitoring.
