Thanks for your report.  There does indeed seem to be a problem but, as can be seen if you run your test from SO (please attach it to this issue!) with a current python.org 3.6.x installer for macOS which uses the same build infrastructure as the 3.7 and 3.8 installers, the results are correct.  The macOS Pythons from python.org are built to run on a range of OS versions: these days macOS 10.9+ or 10.6+.  Your test also fails when run on these earlier systems with 3.7.0 or later but not 3.6.8.  There were a number of changes made in 3.7 to the time module and underlying code in Python, specifically Python/pytime.c, so my guess is that the changes are depending on some feature or change that is in later versions of macOS since the expected results are obtained when built directly on and run on a current macOS version.  That needs to be fixed for 3.7.3.

I had time to run a quick check building on earlier macOS versions. It looks like the incorrect results show up when building on macOS 10.11.x and earlier.
10.12 through 10.14 have the correct results.  I don't have time to investigate further today.

BTW, it would be a good idea to adapt your test program as a test case, i.e. ensure the results are "close" to each other.