"....a day to honour the greatest wizard of this or any age."
-- letter from Harold Skively to the Daily Prophet (DP1)
Mr Skively in his letter makes a case for a wizarding public holiday to honour the wizard Merlin, but ruins it by mentioning that what he would really like is a day off that would fall in the summer months. The editor of the Daily Prophet sees through this (DP1).
In the UK, there is only the Summer Bank Holiday on the last Monday of August as a public holiday between the Spring Bank Holiday at the end of May and Christmas Day in December - quite a long stretch (gov.uk). It is not just Wizards who would appreciate another public holiday going on the calendar.
Although the date printed on the first Daily Prophet Newsletter (DP1) is 31 July 1998, the timeframe for this event is 1992-1993.
From the Web
Writing by J K Rowling on Pottermore:
Harry Potter Wiki: Merlin