%!TEX pdflatex

\documentclass{beamer}
\usepackage{pictochrono}
\usepackage{pgffor}

\newcommand\secondtominutesecond[1]{%
	\xdef\tmpminutes{\fpeval{trunc((#1)/60,0)}}%
	\xdef\tmpsecondes{\fpeval{(#1) - 60*(\tmpminutes)}}%
	%minutes
	\ifnum\tmpminutes<10\relax0\fi\tmpminutes%
	:%
	\ifnum\tmpsecondes<10\relax0\fi\tmpsecondes%
}

\begin{document}

\foreach \i in {90,89,...,0}{%
\begin{frame}
	\transduration{1}
	\hfill{\LARGE \secondtominutesecond{\i}}
	
	\vfill
	
	Question n°1 : blabla
	
	Question n°2 : blabla
	
	Question n°3 : blabla
	
	\vfill\null
\end{frame}
}

\end{document}