Rick's newest Scandinavia talks about several ways to cruise the Norway in a Nutshell route (see below). I'm not clear on whether the Fjord 1 ferry is a "4.5-hour round-trip" or whether "the cruise ends in Gudvangen."
There are several ways to cruise it: You can take the Fjord 1 ferry, described earlier as part of the Norway in a Nutshell trip (4.5-hour round-trips departing Flåm in peak season at 9: 00, 11: 00, and 13: 20, 400 kr; these should also stop in Aurland and Undredal— make sure the crew knows that you want to get off, and that the cruise ends in Gudvangen).
Steves, Rick (2015-06-23). Rick Steves Scandinavia (Kindle Locations 6038-6040). Avalon Travel. Kindle Edition.