\documentclass[clock]{slides}
\begin{document}
\begin{slide}   Titre                 \end{slide}
\addtime{10}
\begin{slide}   Transparent 2         \end{slide}
\addtime{90}
\begin{overlay} Transparent 2bis      \end{overlay}
\addtime{20}
\begin{slide}   Transparent 3         \end{slide}
\addtime{60}
\begin{note}    D\'ebut de projection \end{note}
\addtime{600}
\resettime
%equivaut a \settime{0}
\begin{slide}   Transparent 4         \end{slide}
\addtime{180}
\begin{slide}   Conclusion            \end{slide}
\addtime{60}
\begin{note}    C'est fini !          \end{note}
\end{document}
