You also need to know where the satellites are meant to be at any one time. That means a stable orbit. Starlink isn't really designed for that.
It then also needs to be signed/secure so that its not spoofed.
Then your signal that your measuring time from needs to be transmitted often enough and robust enough. Plus your time source on the transmitter needs to be accurate enough.
It might be possible with starlink, but you'd also have to trust musk....
gps is 31 total satellites 12,000 miles up
starlink is 10,000 satellites at ~ 300 miles. (and what orbit?)
EDIT: I found this:
-- starlink:
"In any given place there are 3-4 Starlink satellites visible at a time"
https://news.ycombinator.com/item?id=42445512 :)
in december 2024, there were 4,000 starlink satellites in orbit
so starlink is ~ 8 at all times?
-- GPS:
This 24-slot arrangement ensures users can view at least four satellites from virtually any point on the planet.
- https://www.gps.gov/space-segment