The third Thursday of the third week was March 5th, also known as 'Start of Spring Thunder'.
'Start of Spring Thunder' signifies the idea that hibernating insects are startled by the thunder of early spring and leave their burrows. Lying dormant for a winter, alongside the warmer weather and frequent spring thunder, the insects crawl out of their dens, also awakening the vitality of the land.
Of course, the above is just what's supposed to happen 'in theory'. But like the 'rational person' in economics, the situation in theory often deviates in practice.
For instance, during the winter of 08-09, due to the abnormal silence and return of the tide from the previous year, the time insects spent in hibernation underground was significantly shortened. Many had already swarmed out of their caves with the onset of spring, resulting in the 'Start of Spring Thunder', although the lead characters of this solar term had become supporting players by the actual day.