Near the end, Elisa says to Tom "I don't understand how you could have lived back then (in 995 A.D.) and still be alive today." He explains that time passes differently on Avalon. Every hour on Avalon is one day everywhere else. This translates to 1 day on Avalon equalling 24 days everywhere else. And 1 year on Avalon will also be equal 24 years everywhere else as well. Since 1,000 years have passed out here that means only 42 years, approximately, have passed on Avalon.
This episode takes place in 994, 995 and 1995.