1. At Thanksgiving Americans eat a roast turkey.
2. On Thanksgiving Americans eat a roast turkey.
(Which preposition, do we have to use 'at' or 'on' before 'Thanksgiving'? Are both OK?)
3. on/at the weekend
4. on/at Sunday
5. on/at New Year's Day
6. on/at Christmas
7. on/at the weekend
8. on/at November 1st
9. on/at Labor Day
(Can we use both prepositions in all cases? Or which preposition do we have to use?)
1 and 2 -- Either "At" or "On" works well, but I'd remove "a" in front of "roast turkey."
3, 4, 5, 7, 8, and 9 - use "on"
6 - on Christmas OR at Christmastime