Free Throws with 0.00 showing on the clock...

[Adam]

"Definite" does not mean "exact." "Exact" is neither in the rules nor is it a practical guideline. If you want exact knowledge, you'll never make a correction in the time.
You can definitely know that at least 5 seconds should have come off, even if you know it should have been closer to 15. Take the 5 off.

Now, if you're unsure, talk to the assigner/rules interpreter relevant to your assigned games. If your assigner happens to be Jurassic, well, you know what to do....