Network protocols are another matter, since they have to be understandable by a foreign machine of unknown architecture.
But as far as I recall (admittedly it's been many years), internal representations of time on Symbolics machines were all bignums.
Boxing/unboxing wasn't such an issue since the hardware had type tags and would handle a lot in microcode.
But, as I said, it's been 40+ years since I had to know this in any detail.