\documentclass[a4paper]{article}
\usepackage{german}
\usepackage[utf8]{inputenc}

\usepackage{pgfplots}
\usepgfplotslibrary{dateplot}

\usepackage{pgfplotstable}
\usepackage{booktabs}
\usepackage{array}
\usepackage{colortbl}


\begin{document}


\begin{tikzpicture}
  \begin{axis}[
  xmin=2009-08-18 09:00,
  xmax=2009-08-19 6:0,
    date coordinates in={hist/data},
    date coordinates in={x},
	plot coordinates/math parser=false,
    xticklabel style=
		{rotate=90,anchor=near xticklabel},
   xticklabel=\day. \hour:\minute,
    date ZERO=2009-08-18,% <- improves precision!
  ]
  \addplot+[
  hist={bins=2,data value=\pgfkeysvalueof{/data point/x}}] coordinates {
    (2009-08-18 09:00,  050)
    (2009-08-18 12:00,  100)
    (2009-08-18 21:30,  040)
    (2009-08-19,        020)
    (2009-08-19 3:00,   000)
    (2009-08-19 6:0,    035)
  };
  \end{axis}
\end{tikzpicture}


\end{document}

