I'v heard if its wraped up good with a few towels in a well insulated cooler that is pre-warmed with hot water 12+hours. I've not tried pre-warming the cooler but just wrap the meat in 3 layers of foil and wraped in towels and put in a good air tight cooler and rest for 3 hours and the meat is still to hot to handle bear handed. I would not be afraid to go 6 hours, thats the way I do it but if need to go longer I would check internal meat temp if its above 140 your good if its close to 140 I would put it in the oven at a low temp around 165 to keep warm till serving.