\documentclass{standalone}
\usepackage{tikz,pgfplots}
\usepackage{siltex}
\usetikzlibrary{arrows.meta,positioning,calc,fadings}
\pgfplotsset{compat=1.17}
\begin{document}
\begin{tikzpicture}
    \pgfmathsetlengthmacro{\xbarvalue}{-3mm}
    \pgfmathsetlengthmacro{\barwidthvalue}{4mm}
\begin{axis}[
    xbar=\xbarvalue,
    bar width=\barwidthvalue,
    xmin=0,
    xmax=21,
    width=85mm,
    height=75mm,
    enlarge y limits=0.15,
    legend style={at={(0.98,0.95)},
        anchor=north east,legend columns=-1},
    xlabel={Days},
    symbolic y coords={Software Development,Development Cycle 2,Development Cycle 1,Test Protocol,Feature Definition,Initial Design,Specifications,Problem Description},
    ytick=data,
]
    \addplot[draw=red,fill=red!40] coordinates {(2,Problem Description) (3,Specifications) (3.5,Initial Design) (13,Feature Definition) (0.5,Test Protocol) (3,Development Cycle 1) (17,Development Cycle 2) (20,Software Development)};
    \addplot[draw=blue,fill=blue!40] coordinates {(2,Problem Description) (3,Specifications) (5,Initial Design) (6,Feature Definition) (1,Test Protocol) (3,Development Cycle 1) (13,Development Cycle 2)};
    \legend{Time Spend,Time Planned};
    \pgfmathsetlengthmacro{\baroffset}{\barwidthvalue+\xbarvalue/2}
    \pgfmathsetlengthmacro{\smeer}{7mm}
    \node (a) at ($(axis cs:3,Development Cycle 1)-(0.1mm,0mm)+(0mm,\baroffset)$) {};
    \node (b) at ($(axis cs:3,Development Cycle 1)-(0.1mm,0mm)-(0mm,\baroffset)$) {};
    \fill[white] (a) rectangle ++(\smeer,-\barwidthvalue-1mm);
    \fill[red!40,path fading=east] (b) rectangle ++(\smeer,1mm);
    \fill[blue!40,path fading=east] (a) rectangle ++(\smeer,-\barwidthvalue);
    \draw[white] ($(a)$) -- +(\smeer,0mm) ++(0mm,-\barwidthvalue) -- +(\smeer,0mm);
    \draw[white] ($(b)$) -- +(\smeer,0mm); 
    \draw[blue,path fading=east] ($(a)$) -- +(\smeer,0mm) ++(0mm,-\barwidthvalue) -- +(\smeer,0mm);
    \draw[red,path fading=east] ($(b)$) -- +(\smeer,0mm); 
\end{axis}
\end{tikzpicture}
\end{document}
