the Bon Festival and New Year
Refers to the two biggest traditional holidays in Japan, often used to describe something that happens only on very special occasions, like 'once in a blue moon'.
It's as busy as if the Bon Festival and New Year came at the same time.
two great things at once; double delight
Idiomatic expression likening a rare, doubly happy event to having both major holidays simultaneously.
Getting a raise and a bonus at the same time is like having the Bon Festival and New Year together.
Compound of 盆 (Bon Festival) and 正月 (New Year), two major Japanese holidays. The idiomatic sense comes from the idea of two rare, joyous occasions coinciding.