This is, according to the Guinness Book of World Records, the biggest firework every launched. The YouTube notes say that it holds the record for “Largest Aerial Firework”, an is a 62 inch firework ignited over Steamboat Springs Colorado two years ago.
There’s a time delay because, of course, the speed of sound is slower than the speed of light. One punctilious commenter said this:
Fun fact: They are standing around 3 km away Sound is coming 8sec late. Speed of sound 343 m/s 343*8= 2744m so 3km approx.
Here’s another video by someone who filmed it. It shows the pyrotechnic itself (it weighed over a ton!) as well as part of its construction, its launching, and the Guinness award.