Usage patterns
〈場所〉の定休日は〈時〉だa place's regular closing day is [day]
This café's regular closing day is Tuesday.
定休日で休むto be closed for the regular holiday
We're closed today because it's our regular closing day.
定休日を確認するto check a shop's regular closing day
I checked the shop's regular closing day before going.
〈時〉を定休日にするto set a day as the regular closing day
Many shops set Wednesday as their regular closing day.