I suspect it just means that Garmin decided that the older version from the chip vendor was working better for them
Now update to 9.50, and really time downgraded to 2019 0122113018a
The MTK firmware is 35345 for both. The firmware is the same.
Whatever “build time” is, it’s not the firmware.
Why recompile the firmware? Boredom?
You don't know what "build time" is referring to.
Why speculate about something you know little about and likely doesn't matter?
Maybe, it's the date the chip was made.