date value
1986-03-01 0.11
1986-06-01 0.45
...
2016-03-01 0.78

usepackage{pgfplots}
usepackage{amsthm, amsfonts, amsmath, amssymb, mathrsfs, enumerate,graphicx}
usepackage{subcaption}
usepgfplotslibrary{dateplot}
usepackage{filecontents}
pgfplotsset{height=5cm,width=8cm,compat=newest}
usepgfplotslibrary{dateplot}

begin{figure}[H]
begin{subfigure}{.5linewidth}centering
begin{tikzpicture}
begin{axis}[legend style={at={(0.5,-0.35)},anchor=north},
  date coordinates in=x,
  x tick label style={/pgf/number format/1000 sep=},
  xticklabel={year},
  ylabel=,
  xlabel=Time,
  enlargelimits=0.10,
  legend columns=1,
]
addplot[no markers, color=black]
  table [x=date, y index=1] {msardhp.dat};
legend{}
end{axis}
end{tikzpicture}
end{subfigure}%
caption{}
end{figure}

documentclass{article}
usepackage{pgfplots}
usepgfplotslibrary{dateplot}
pgfplotsset{height=5cm,width=8cm,compat=newest}
begin{document}
begin{tikzpicture}
begin{axis}[legend style={at={(0.5,-0.35)},anchor=north},
  date coordinates in=x,
  xticklabel={year},
  date ZERO={1986-01-01},
  xtick={%
    1986-01-01,
    1992-01-01,
    1998-01-01,
    2004-01-01,
    2010-01-01,
    2016-01-01%
},
%  ylabel=,
  xlabel=Time,
  enlargelimits=0.10,
  legend columns=1,
]
addplot[no markers, color=black]
  table [x=date, y index=1] {
date value
1986-03-01 0.11
1986-06-01 0.45
2016-03-01 0.78
};
legend{}
end{axis}
end{tikzpicture}
end{document}