The phrase "just 1.5 billion years after the Big Bang time, time ran five times slower than it does today, 13.8 billion years later" seems to make about three self-referential loops around itself. What does 1.5 billion years mean if time ran slower? Is it slow years or fast years, and from what frame of reference would you even tell the difference? What does "slow" even mean, isn't speed measured in relation to time passing?
If you're comparing two physically separated frames of reference it makes sense to talk about "this many seconds here corresponds to that many seconds over there". But when you're talking about the speed of time for the entire universe, how do you form such a ratio?
If you're comparing two physically separated frames of reference it makes sense to talk about "this many seconds here corresponds to that many seconds over there". But when you're talking about the speed of time for the entire universe, how do you form such a ratio?