Using arithmetics on macros in pgf-axis-environment to specify x-ticks with TeXLive2016

Question

The Problem: I want to compile the figure below with TeXLive2016 compatibility. I know this is kind of outdated, but apparently it is used by arxiv. The MWE compiles with TeXLive2019, but not when I switch to TeXLive2016 (e.g. on Overleaf, where you can easily change the TeXLive version). I have located the error to be caused by the xtick definition in the axis environment. Somehow, the macros are not correctly parsed here, while they are perfectly well parsed everywhere else.

The error that is thrown is:

! Package PGF Math Error: Could not parse input '0.7+1.0' as a floating point n umber, sorry. The unreadable part was near '+1.0'.. See the PGF Math package documentation for explanation. Type H for immediate help. ...
l.49 \end{axis}

What I've tried:

• use xfp package -> compatibility issues
• use fp package -> did not work to construct an evaluated list with \FPeval
• create a style for the right x-tick positions -> didn't solve the problem
• use /.expanded on xtick-> didn't solve the problem
• use \pgfmathparse in combination with \pgfmathresult-> not available in TeXLive2016

Related Questions: Here is, what I think are related questions to my problem, although I have not been able to distill an answer from that.

• Q1
• Q2
• Q3
• Q4
• Q5

MWE:

\documentclass[preview]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{graphics}
%
\usepackage{tikz}%drawings like geometries
\usetikzlibrary{calc,matrix,positioning}
\usetikzlibrary{decorations.pathmorphing}
%
\usepackage{pgfplots}
\pgfplotsset{
    ,compat=1.12
    }
%----------------------------------------
\begin{document}
%
\begin{figure}[ht]
    \centering
    \begin{tikzpicture}
    %Define Parameters
    \newcommand\tmin{0.7}
    \newcommand{\dtmax}{\dtstart}
    \newcommand{\dtstart}{1.0}
    \newcommand{\T}{2.0}
    \newcommand{\zmin}{3.0}
    \newcommand{\dvstart}{0.8}
    \newcommand{\vstart}{1.0}
    \newcommand{\zmax}{9.0}
    \newcommand{\g}{0.6}
    \newcommand{\keff}{1.0}
    %
    \begin{axis}[
        xlabel={t}, xlabel style={at={(1,0)}, anchor=west},
        ylabel={z (m)}, ylabel style={rotate=-90,at={(0,1)}, anchor=south},
        xmin=0.0, xmax=\tmin+\dtstart+2*\T+2*\dtmax,
        xtick={0,\tmin,\tmin+\dtstart,\tmin+\dtstart+\T,\tmin+\dtstart+\T+\T,\tmin+\dtstart+\T+\T+\dtmax},%
        xticklabels={$0$,$t_{start}$,$t_0$,$t_0+T$,$t_0+2T$,$t_{end}$},%
        ymin=0, ymax=\zmax,
        axis lines = left,
        y=1.cm,
        x=1.cm,
        ytick={0,1,...,12},
        legend pos=north west,
        %grid=both,
        ymajorgrids=true,
        grid style=dashed,
        ]
    \end{axis}
        %Laserbeams
        \draw[decorate, decoration = snake, very thick, red, opacity=0.5]
        ({\tmin + \dtstart},0) to ({\tmin + \dtstart},{.9*\zmax}) node[above] {$\pi/2$};
        \draw[decorate, decoration = snake, very thick, red, opacity=0.5,] 
        ({\tmin + \dtstart+\T},0) to ({\tmin + \dtstart + \T},{.9*\zmax}) node[above] {$\pi$};
        \draw[decorate, decoration = snake, very thick, red, opacity=0.5,] 
        ({\tmin + \dtstart + 2*\T},0) to ({\tmin + \dtstart + 2*\T},{.9*\zmax}) node[above] {$\pi/2$};
    \end{tikzpicture}
\end{figure}
\end{document}