Some players brought something to my attention: does speeding up time cause your meditation bar to fill more quickly?
Based on my tests, no. They both took 15 minutes exactly to fill.
I let one blockhead meditate while time was sped up and timed it, and I did the same with a blockhead while time wasn’t sped up. They both took 15 minutes, so no matter when you meditate, it will take that long to finish.