When Beowulf fights Grendel's mother, how long is he gone and how does this affect the morale of the men on the shore?

When Beowulf descends through the mere to the lair of the monsters, Hrothgar, his Scyldings, and Beowulf’s Geats wait on the shore of the lake for Beowulf to return. After the water of the lake becomes mixed with blood, we are told that old men, likely referring to Hrothgar and his advisors, begin to talk about Beowulf not returning, which indicates they believe that he has been killed. Following the ninth hour of the day (likely 3:00 pm), Hrothgar and his men depart from the shore, leaving only the Geats to wait for Beowulf. Further, we are told that the Geats’ wait is one of sorrow, as they wish but do not necessarily believe that their lord will return victorious.
The specific length of time that Hrothgar, his men and Beowulf’s men wait for Beowulf to return is not provided by the poem. We know that the expedition to track Grendel’s mother and find Aeschere's body likely begins in the early morning, as Beowulf is summoned by Hrothgar at daybreak. We are told that, after reaching the lake, Beowulf takes a large portion of the day to make his descent to the cavern in which Grendel’s mother awaits him, but it is unclear whether we are meant to take that line as literal, given the impossibility of him remaining under water for a large portion of the day, or as a hyperbole. Finally, we know that Hrothgar and the Scyldings leave the lake’s shore at the ninth hour of the day, which likely means 3:00 pm (nine hours after 6:00 am). We do not know how long the Geats remain waiting after the Scyldings leave. However, if we presume that the journey to pursue Grendel’s mother takes some time to assemble, and that reaching the lake while tracking the passage of Grendel’s mother also takes some time, we would probably not be out of line to guess that the search party reaches the lake between 8:00 and 10:00 am. This would mean that the Scyldings likely wait at least five hours for Beowulf to return, with the Geats remaining some undetermined time longer.
Even a conservative estimate of the time for which the Scyldings and the Geats await Beowulf’s return is problematic with respect to what we would expect to be a plausible time frame for the physical accomplishments of Beowulf, first in swimming down to the lair of Grendel’s mother, then in fighting and defeating her. One idea of how to resolve this apparent time discrepancy is to interpret the time references to be symbolic of something taking a long time rather than referring to actual measures of time. Another interpretation is that once Beowulf sinks below the surface of the lake, time for him moves differently than for those waiting for him on the shore.
Regardless of how we calculate the time or interpret what the specific time references might mean, we know that those waiting hold their vigil for a long enough time that the Scyldings give up hope and leave the shore, believing Beowulf to be dead. And we know that the Geats wait longer but in sorrow, for although they wish for his return, they do not appear to truly believe that he will return. But even in sorrow, the Geats do wait for Beowulf, and that wait, however long, and their hope beyond what might have been reasonable to hope, is rewarded.