\documentclass[12pt]{article}

\usepackage{timeline}

\begin{document}
\thispagestyle{plain}

\section*{Example of opacity}

I added a 6th argument to timebar to select which step to apply to show years.
I added an optionnal argument for opacity of labels. 
It could be nice to centralise this argument as a single value, but don't know where to put it.

\begin{timeline}
 \timebar[2]{|}{0}{2000}{2013}{1}{}

  \entry{2002}{entry}{no opacity}
  \entryshift{2003}{entryshift}{no opacity}{4mm}
  \flipentry{2004}{flipentry}{no opacity}
  \flipentryshift{2005}{flipentryshift}{no opacity}{4mm}

  \entry[0.5]{2008}{entry}{opacity}
  \entryshift[0.5]{2009}{entryshift}{opacity}{4mm}
  \flipentry[0.5]{2010}{flipentry}{opacity}
  \flipentryshift[0.5]{2011}{flipentryshift}{opacity}{4mm}
\end{timeline}

A project I would love to do is also understand how to had a caption !


\newpage

\end{document}