Letting a deer lay overnight will not spoil the meat most of the time. If the night temp is low enough, the meat will be perfectly good. I shot a buck last season in September. It was still a bit warm but I knew the shot was a bit far back. I followed the trail for about 100 yards before pulling out. The next morning I went back with a buddy and we were able to recover the deer. The low that night was in the upper 60s to low 70s and the meat was fine.