Average Ausbund hymn — 8-12 stanzas. At 5 minutes per stanza, that's 40-60 minutes for one hymn. Service includes 3-4 hymns = 2-3 hours of singing.
Patience
For the Amish, a long hymn isn't an ordeal but patience practice. Gelassenheit. You don't rush because there's nowhere to rush. Time isn't money (worldly). Time is God's gift. Spending it on singing is right.
Children
Children sit quietly. From age 3-4. Two to three hours. No toys, no books, no screens. How? Habit. By 6, a child doesn't know it could be otherwise.