Although Bill and Ted frequently said both “party time” and “excellent”, Wayne’s World wrote “Party time, excellent” into their theme song. So, the phrase “Party time, excellent!” started with Wayne’s world.

But really, the ninja turtles were saying all of that before any of those guys.

Bill & Ted is “Be excellent to each other, and party on, dudes!”

I’m pretty sure “Party time! Excellent!” isn’t in Bill and Ted at all.
It’s exclusively Wane’s World.

My man, you need to rewatch both those movies back to back to see how wrong you are.

Really looks like what we have here is a case of the zeitgeist.

Bill and Ted’s Excellent Adventure: Released to theaters February 17, 1989

https://en.m.wikipedia.org/wiki/Bill_%26_Ted's_Excellent_Adventure

Wayne’s World started as an SNL skit, first appeared February 18, 1989.

https://en.m.wikipedia.org/wiki/Wayne's_World

Although Bill and Ted, as a production, goes back to 1987.

I never knew B&T to say that phrase. Their faves were always “Party on, dudes” and the like.

I’m pretty sure Wayne’s World skit on SNL in the mid 80’s is where the phrase was born.

It all came from SNL and the characters they played on there.