For regulatory purposes, milliseconds are negligible. FINRA allows for up to 3 seconds of divergence from standard time sources.

For deep alpha signals, a millisecond is pretty negligible (especially when you are calculating minute or 10 minute bars).

For microstructure trading strategies, since the timing doesn't manipulate the book (which is where most microstructure trades derive alpha from), the effect is similarly negligible.

And for cross-exchange and cross-asset arbitrage, where microseconds may seem matter (regnms), slight drifts are permissible insofar as you can plausibly argue that even if the clock is slightly off, your view of the market is internally consistent

Shift of the clock signal by milliseconds may well not matter, for sure, assuming all relevant clocks are affected.

You can make a million dollars in a millisecond.

I wasn't being sarcastic.