If you need to have an excused absense, it's not the end of the world. Pref is important, but I've always seen it as more important for the PNM for the chapter. An excused absense is not usually going to count against you or anything, that's why it's excused
And I know some people are saying to work around it, and if you can comfortably, great. But don't skip your obligations if they're that high of a priority to you.