Big Sur b4. What is meant by "Updating to macOS Big Sur 11 beta from previous versions of macOS might take significantly longer than expected." ?

In the release notes for Big Sur b4, we can find the same note as for b4:

"Updating to macOS Big Sur 11 beta from previous versions of macOS might take significantly longer than expected."

What does "significantly longer" mean? 10 minutes ? 30 minutes ? 2 hours?

From what I'm observing, updating from b3 to b4 is a bad as updating from b2 to b3. The "Preparing macOS Big Sur beta X…" step is taking an eternity to complete while the fans are spinning crazily. No processes are reported to use a lot of CPU time in Activity Monitor.

Question:

Do we need to erase the disk and install a fresh copy of Big Sur betas for each new beta?
Big Sur b4. What is meant by "Updating to macOS Big Sur 11 beta from previous versions of macOS might take significantly longer than expected." ?
 
 
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