9:30PM UTC and 6:30PM PDT are not the same time. 9:30PM UTC would be 2:30PM PDT.
I'm guessing that you mean 9:30PM EDT / 6:30PM PDT (which would be 1:30AM UTC btw), as those times match and are consistent with previous boss spawn time schedules, but I am making this post to make 100% sure before I assume anything.
Or are the times listed different because the first one is to represent the spawn time on EU and the 2nd the spawn time on NA?