Is the mouthpiece honeymoon period a real thing?

Absolutely!  This is not just with mouthpieces.  Anytime you make a change with your equipment or body, an adjustment period is needed, which your embouchure is no different. The honeymoon period typically sets in 1-2 weeks after the adjustment or change. If you notice a dramatic change in articulation, endurance, or flexibility you may want to work with your teacher or professor to understand better how the change is affecting you.

Humans are creatures of habit - when you've been playing an instrument and mouthpiece for a very long time, you will have adjusted to that setup.  When you then change the instrument or mouthpiece, it can be hard to break old habits in order to find new habits that work better.  Spending the first 1-2 weeks is crucial to see how the new equipment helps or changes how you approach your playing.