Does a 0.1 PSI drop in 24 hours indicate a leak in gas piping?
Home Flex's CSST manual http://homeflex.com/downloads/HOME-FLEX_Installation_Manual.pdf tells you to test at 150% of the product's operating pressure.  A good rule of thumb is always check the product manual first.
When people say 20% of a gauge's capacity, they don't mean over-pressure the gas pipe system; they actually mean get a different gauge if you need to.  Don't, for example, use a 90 PSI gauge to test a 3 PSI gas system; it's not designed to be sufficiently accurate for the test.  The reason people say test at minimum 20% on the gauge is the NFPA 54 fuel gas code §8.1.4.1 says shall have a range such that the highest end of the scale is not greater than 5 times the test pressure.  In any event, I believe you have the correct gauge for your project.
Regarding the test duration, your local building official is the authority on this; but NFPA says for a residence the test duration shall be a minimum of 10 minutes.  The duration of the test shall not be required to exceed 24 hours.  It further says Any reduction of test pressures as indicated by pressure gauges shall be deemed to indicate the presence of a leak.  Sucks, right?  The better your equipment and the more diligent you are, the more likely you chase a ghost, because the code is non-specific.
That's why I'm suggesting ask your building inspector.  He or she will probably tell a story about some local system they can't believe never exploded, and tell you the 0.1 PSI is okay.  Nobody here wants to be the one to say that!  :D