This is an excerpt from the technical publication for one of the now discontinued Kodak black and white papers:
Wash for at least 1 hour in running water at 10 to 30°C (50 to 86°F), interleaving the prints carefully and frequently. The wash-water flow rate should provide at least one complete change of water in the container every 5 minutes. The KODAK Automatic Tray Siphon provides proper movement and agitation during washing.
Avoid prolonged washing or soaking times to minimize physical damage to the prints and to maintain the effect of the optical brightener in the paper.
To reduce time and conserve water, use KODAK Hypo Clearing Agent before washing. Transfer the prints, with or without a previous rinse, to the clearing agent. With Hypo
Clearing Agent, wash for 10 minutes with agitation and normal water flow."
Note the water flow recommendation - you can probably attain a complete change of water every 5 minutes by adding enough water to fill the tray every 3 minutes. So if you have a 3 litre tray, an hour wash may take less water than you think.