\newcommand{\x}{\parbox[0pt][2.7cm][c]{3.7cm}{\hspace{3.7cm}} }
\newcommand{\xT}{\parbox[0pt][1.6cm][c]{1.9cm}{\hspace{3.7cm}} }
% --- Farbdefinitionen ----------------------------------------
\definecolor{hellgrau}{rgb}{0.95,0.95,0.95}

%\begin{sidewaystable}
%\begin{addmargin}[-2mm]{0cm}

%\begin{center}
%\begin{tabular}{|c|c|c|c|c|c|}
%\hline Zeit & Montag & Dienstag & Mittwoch & Donnerstag & Freitag \\
%\hline 8-10  & \x & \x & \x & \x & \x \\
%\hline 10-12 & \x & \x & \x & \x & \x \\
%\hline 12-14 & \x & \x & \x & \x & \x \\
%\hline 14-16 & \x & \x & \x & \x & \x \\
%\hline 16-18 & \x & \x & \x & \footnotesize 16:00 : Fachschaftstreffen & \x \\
%\hline ab 18 & \x & \x & \x & \x & \x \\
%\hline
%\end{tabular}
%\end{center}

%\end{addmargin}
%\end{sidewaystable}

\vspace{23.6cm} % ein Korrekturabstand wg. Drehen
\begin{center}
\begin{rotate}{90}
\begin{tabular}{|c|c|c|c|c|c|}
\hline \cellcolor{black} \xT
	& \cellcolor{black} \textcolor{white}{\textbf{Montag}}
	& \cellcolor{black} \textcolor{white}{\textbf{Dienstag}}
	& \cellcolor{black} \textcolor{white}{\textbf{Mittwoch}}
	& \cellcolor{black} \textcolor{white}{\textbf{Donnerstag}}
	& \cellcolor{black} \textcolor{white}{\textbf{Freitag}} \\
\hline 8:00-10:00  & \x & \x & \x & \x & \x \\
\hline  \cellcolor{hellgrau}10:00-12:00 &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x \\
\hline 12:00-14:00 & \x & \x & \x & \x & \x \\
\hline  \cellcolor{hellgrau} 14:00-16:00 &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x \\
\hline 16:00-18:00 & \x & \x & \x & \footnotesize & \x \\
\hline  \cellcolor{hellgrau} 18:00-20:00 &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x &  \cellcolor{hellgrau} \x \\
\hline
\end{tabular}
\end{rotate}
\end{center}