Pgfplots: xtick is ignored with ybar interval

Question

I have a problem with creating a bar plot of demand during a day. My x-coordinates are in "minutes from midnight", but I want to show the time of day on the x-axis at my specified spots (e.g., 6:30 am instead of 390 minutes). xtick and xticklabelsshould do this for me. And they do, when I do not have ybar interval=1, but then it is no longer the right type of plot.

My code is the following:

\documentclass{article}
\usepackage{pgfplots}
\begin{document}
\begin{figure}
    \centering
    \begin{tikzpicture}
        \begin{axis}[
            xtick={390,540,720,900,1020},
            xticklabels={6:30,9:00,12:00,15:00,17:00},
            ylabel=Required staff,
            xlabel=Time of day,
            ybar interval=1,
            width=0.8\textwidth,
            height=5cm,
            axis lines=left,
            ymin=0
        ]
            \addplot 
                coordinates {(390,1) (450,2) (510,3) (570,6) (720,3) (735,2) (780,3) (795,4) (930,2) (960,1) (1020,1)};
        \end{axis}
    \end{tikzpicture}
\end{figure}
\end{document}

and it produces:

Outcommenting ybar interval=1, results in:

Answer 1

The manual (pag. 87 and 320 in my version) says that ybar interval is installed only on a per-plot basis. It messes with the ticks definition if you set it in the axis.

I would add a enlarge x limits=0.05, enlarge y limits=upper to the axis options, to have a bit of breathing space on the axis.

To use the deault coloring for the diagrams, you can use the generic ybar style, and then addplot+:

\documentclass{article}
\usepackage{pgfplots}\pgfplotsset{compat=1.13}
\begin{document}
\begin{figure}
    \centering
    \begin{tikzpicture}
        \begin{axis}[
            ybar, %% installs bar cycle list also
            xtick={390,540,720,900,1020},
            xticklabels={6:30,9:00,12:00,15:00,17:00},
            ylabel=Required staff,
            xlabel=Time of day,
            width=0.8\textwidth,
            height=5cm,
            axis lines=left,
            ymin=0,
            enlarge x limits=0.05,
            enlarge y limits=upper,
        ]
        \addplot+ [ybar interval]
                coordinates {(390,1) (450,2) (510,3) (570,6) (720,3) (735,2) (780,3) (795,4) (930,2) (960,1) (1020,1)};
        \end{axis}
    \end{tikzpicture}
\end{figure}
\end{document}

Answer 2

You could add a second axis environment with the same dimensions:

\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=1.14}% <- current version is 1.14
\begin{document}
\begin{figure}
    \centering
    \begin{tikzpicture}
        \pgfplotsset{
            xmin=390,xmax=1020,
            width=0.8\textwidth,
            height=5cm,
            axis lines=left,
            ymin=0,ymax=6
        }
        \begin{axis}[
            xtick={390,540,720,900,1020},
            xticklabels={6:30,9:00,12:00,15:00,17:00},
            ylabel=Required staff,
            xlabel=Time of day
        ]
        \end{axis}
        \begin{axis}[
            axis lines=none,
            ybar interval=1,
            xtick=\empty,
        ]
            \addplot 
                coordinates {
                    (390,1) (450,2) (510,3) (570,6) (720,3) (735,2)
                    (780,3) (795,4) (930,2) (960,1) (1020,1)
                };
        \end{axis}
    \end{tikzpicture}
\end{figure}
\end{document}