The governor of California can turn around an interim appointment pretty quickly if he so chooses; there's some static around a prior promise to appoint a Black woman, which most people viewed as effectively a promise to Representative Barbara Lee. She has since declared candidacy for that Senate seat--as Feinstein was not going to run for re-election--and Newsom (understandably, IMO) doesn't want to hand the keys to a running candidate, out of fairness to the also-quite-reasonable alternate candidates.

That said, I wouldn't expect it to prevent a pretty quick replacement if Senate business demands it, so it likely won't be a significant impact from a political or operational perspective.