In British English, the preposition at is used for the following festivities:
this holiday season includes Christmas Eve, Christmas Day, and St. Stephen's Day which is on 26 December (also called Boxing Day).
The Easter period includes Good Friday, Easter (which is always on a Sunday) and Easter Monday
at New Year's
this refers to the period around New Year's Day. Some people begin celebrating early on New Year's Eve (in Scotland this day is known as Hogmanay) and some don't stop partying until late into the New Year.
Note that the preposition on refers to a specific date or day, thus we may say
- What are you doing on New Year’s Day? (January 1)
- What are you doing at New Year’s? (December 31 – January 1)
- What are you doing on Christmas Day? (December 25)
- What are you doing at Christmas? (December 24 – 26)
In the case of the Chinese holiday, Dragon Boat Festival, whose date is fixed on the 5th day of the 5th month of the traditional Chinese calendar, this means it changes every year. According to Wikipedia, in 2017 the festival occurred on 30th May, but in
2018 it fell on 18th June.
The date of Easter, on the Christian calendar, also changes every year. It occurs on the first Sunday after the first full moon that occurs on or after March 21. For example in 2017, Easter was on 16 April but this year it was on 1 April. Next year it will be on 21 April.
Therefore, in my experience, British English speakers will normally say
- What are you doing at Easter?
- What are you doing on Easter Sunday?
The same “rules” could be applied to the Chinese festival
- What are you doing at the Dragon Boat Festival? (around this period)
- What are you doing on (the) Dragon Boat Festival?
Online, I found examples using both prepositions
- Visiting China at the Dragon Boat Festival…
- The wine is drunk at the Dragon Boat Festival…
- Make a splash at the Dragon Boat Festival
- ABAX look forward to seeing the local people and businesses of Peterborough at the Dragon Boat Festival on Saturday 10th June 2017
- What food do they eat at the Dragon Boat Festival?
- It is a very popular practice to drink this kind of Chinese liquor seasoned with realgar at the Dragon Boat Festival
- Casualties at the Dragon Boat Festival were common in China in the past as opponents could throw stones and sticks at participants.
- Dragon Boat team members gather under the tent as they get ready to race at the Dragon Boat Festival Saturday morning, July 28, 2018 at...
- Today, people still eat zongzi and participate in dragon boat races to commemorate Qu Yuan’s sacrifice at the Dragon Boat Festival (Duan Wu festival) on the fifth day of the fifth month of the Chinese lunar calendar.
on (with and without the article the)
- What activities do Chinese children do on Dragon Boat Festival?
- Believe it or not, legend has it that at midday on Dragon Boat Festival day, you can balance an egg on its end.
- What do people do on Dragon Boat Festival in different regions of China?
- On Dragon Boat Festival, parents also need to dress their children up with a perfume pouch.
- What do Chinese People Eat on the Dragon Boat Festival?
- Zongzi or rice dumplings, is a traditional Chinese food always eaten on the Dragon Boat Festival on the fifth day of the fifth lunar month.
- These [“Jung”, 五月粽 or Zong Zi] are often eaten at breakfast on the festival day which, as a day of rest, tends to start late so rice dumplings for brunch are quite common.
- The custom of eating mianshanzi on the Dragon Boat Festival mainly prevails in Minqin County in Northwest China's Gansu Province.
- Some areas will boil tea eggs and brine eggs to eat on the Dragon Boat Festival.
- On the Dragon Boat Festival, children normally wear scented sachets to ward off evil. A scented sachet is an ornament worn on the front of the dress.