Hi Mari! Yes, this means that the musical was extremely boring. This is also inferred by "6 hours long" and by the addition of the extra "on". https://www.italki.com/harrym

Yes, that's it! :) It means it took a lot longer, and it usually also means that it was boring!

Character development means how the character grows or changes in the story. So, for Squid Game, the character development for Gi-Hun is that at first he is very selfish (he isn't taking care of his family, for example). By the end of the drama, Gi-Hun tries to help the families of his friends that died by giving money to them, and he wants to stop the Squid Game from happening again. Before, he was selfish; now, he is more caring. So that is one example of character development.

to continue on the meaning of dragged on and on

Yes. I agree with Harry. "Dragged on and on" always implies boredom and almost always an excessive length of time.