When using /debug the game prints a message in chat and it also saves profiler results to a file. The "Time span" value in the file is supposedly measured in milliseconds and the value printed in chat is measured in seconds. You notice that the value in the file is 10e9 times larger than the one in chat. So it should write ns (nanoseconds) instead of ms (milliseconds).
Example comparison:
Profiler results (text file): Time span: 16968367420 ms
Game chat: Stopped debug profiling after 16.97 seconds
Environment
Windows 10
Appears to be fixed in the latest snapshot. I did not test in what snapshot exactly it was silently fixed.