Unlikely it’s today, but there were two other times that 8 days separated beta 4 and beta 5. But I think they’re going to spend some extra time fixing some remaining bugs before switching to a weekly schedule.
I think you know this, but it doesn't work that way. Apple engineers don't wake up one morning and say "Well, I was going to push the button on the next beta, but, you know, this one could use a little more polish before I set it loose on the world."
As was said (I think by
@Ansath or
@C DM ) somewhere many posts up the chain, Apple has an internal schedule of public release dates. Absent some showstopping bug, they release on their schedule. There's no "extra time for fixing bugs" there (plus, they're doing that all the time, even on the builds we don't see in the wild). So, Apple is already as certain as it can be not only for the next release date, but the cadence of release dates all the way to the GM. The only thing that will likely change that are unforeseen events or bugs.