Being a Scout Leader and planner of what we call "high adventures"... The time lag is very possible and understandable. They have likely backpacked/hiked into a remote area of the park. They are miles away from any reliable communications and on foot, it may well have taken a couple of hours to get back to make contact with the park rangers.
Trips I have planned into the Boundry Waters Canoe Area (BWCA) have found us 35 miles into the area, in a canoe, that took us 3 days to get there and 3 to get out.. No cell service and NO motorized access (float planes) allowed.
Cell phones? Is this part of being a Boy Scout, hiking without a cell phone in the group?
No cell serviceI guess amateur radio wasn't part of anyone's 'skill set' either; MANY'S the time that was all there was in terms of mobile service, and still remains so in parts of the outback - coverage from mountain top Two Meter repeaters is an excellent way to 'pass traffic'/messages in dire emergencies ...