The chronosys library allows the dd/mm/yyyy format for the \chronoevent command, but not \chronoperiode. According to this post the functionality should be available. It is not.
How could I modify the code of the following timeline as for the Example period to end at, say, 01/07/2011?
\startchronology
[startyear=2010,stopyear=2012,
color=lightgray, height=1ex,width=\hsize,
dates=false, arrow=false]
\chronoperiode[startdate=false,
stopdate=false, color=red, bottomdepth=0pt,
topheight=1ex, textdepth=10pt]{2011}
{2012}{Example}
\stopchronology

chronosysis notoriously resistant to customisation. If it should work, but doesn't, I'd suggest contacting the author. Even if it isn't supposed to work, the author has responded positively to requests in the past. The alternative is to use something other thanchronosys, because that will be much easier than trying to modify the package code. – cfr Oct 28 '23 at 18:17