The longest glide duration for an RC model was a staggering 36 hours and 3 minutes. I discovered this when looking for common glide ratios. It puzzled me for a while, and I decided to look into it.
Usually gliders can hitch a ride on columns of rising air called thermals. As the sun warms the ground, the warm air begins to rise, causing an updraft. Birds and gliders, and unfortunately sometimes rockets, can tap into this rising air and stay aloft for hours. But I had to think about it... 36 hours goes through the night, needless to say, and so obviously there would be no sun out to cause the thermals.
So I did a little bit of research, and found that there is another technique used by gliders to stay aloft: ridge-soaring. As the wind hits a slope, it is deflected upwards, so there is a stream of rising air right over a slope. This world record glide was simply hand-tossed from a slope and kept in the rising air for 36 hours.