Reduce length of arrow from block diagram

Question

In the code below, the arrows going into and out of the block diagram box are too long.

How do I go about reducing the length of the arrows?

CODE:

\documentclass{article}
\usepackage[landscape]{geometry}
\usepackage{amsmath,amssymb,amsthm}
\usepackage{esint}
\usepackage{amsfonts}
\usepackage{blox}
\usepackage{tikz}
\usetikzlibrary{quotes, decorations.pathmorphing, shapes, arrows.meta}
\usepackage[most]{tcolorbox}
\usepackage{colortbl}
\usepackage{xcolor}
\usepackage{mathtools}
\usepackage{enumitem}

\advance\topmargin-1in
\advance\textheight3in
\advance\textwidth3in
\advance\oddsidemargin-1.5in
\advance\evensidemargin-1.5in
\parindent0pt
\parskip2pt
\newcommand{\hr}{\centerline{\rule{3.5in}{1pt}}}

\begin{document}

\newtcolorbox{mybox}[2][]{text width=0.3\textwidth,fontupper=\scriptsize,
fonttitle=\bfseries\sffamily\scriptsize, colbacktitle=black,enhanced,
attach boxed title to top left={yshift=-2mm,xshift=3mm},
boxed title style={sharp corners},top=3pt,bottom=2pt,
  title=#2,colback=white}

%%------------ Hilbert Transform ---------------

\begin{mybox}{Hilbert Transform}
\vspace*{0.5cm}
    % https://tex.stackexchange.com/questions/175969/block-diagrams-using-tikz
\tikzstyle{block} = [draw, fill=white, rectangle, scale=0.9,
    minimum height=1em, minimum width=1em]
\tikzstyle{sum} = [draw, fill=white, circle, node distance=1cm]
\tikzstyle{input} = [coordinate]
\tikzstyle{output} = [coordinate]
\tikzstyle{pinstyle} = [pin edge={to-,thin,black}]

\begin{tikzpicture}[scale=0.8, rounded corners, every node/.style={scale=1}, remember picture,overlay, auto, node distance=2cm,>=latex']

    \node [input, name=input] {};
    \node [block, right of=input] (controller) {h(t)};
    \node [output, right of = controller, name=output] {};

    \draw [->] (input) -- node[name=$x(t)$] {$x(t)$} (controller);
    \draw [->] (controller) -- node{$\hat{x}(t)$} (output);

\end{tikzpicture}
\vspace*{0.5cm}
\end{mybox}

\end{document} 

Answer 1

You are using some deprecated syntax elements:

• \tikzstyle{blabla}=[...] is superseded by \tikzset{blala/.style={...}};
• Relative positioning is much more straightforward with the positioning library.
• On the long run you may also want to abandon the arrows library in favor of arrows.meta.

Glad to see that you're using tcolorbox. As for your question, with positionin it is straightforward to place a node some distance right of som other node, e.g. \node [block, right=1cm of input] (controller) {h(t)};. Note that the position of = has changed compared to what you have, it is now before of.

\documentclass{article}
\usepackage[landscape]{geometry}
\usepackage{amsmath,amssymb,amsthm}
\usepackage{esint}
\usepackage{amsfonts}
\usepackage{blox}
\usepackage{tikz}
\usetikzlibrary{quotes, decorations.pathmorphing, shapes,
arrows.meta,positioning}
\usepackage[most]{tcolorbox}
\usepackage{colortbl}
\usepackage{xcolor}
\usepackage{mathtools}
\usepackage{enumitem}

\advance\topmargin-1in
\advance\textheight3in
\advance\textwidth3in
\advance\oddsidemargin-1.5in
\advance\evensidemargin-1.5in
\parindent0pt
\parskip2pt
\newcommand{\hr}{\centerline{\rule{3.5in}{1pt}}}

\begin{document}

\newtcolorbox{mybox}[2][]{text width=0.3\textwidth,fontupper=\scriptsize,
fonttitle=\bfseries\sffamily\scriptsize, colbacktitle=black,enhanced,
attach boxed title to top left={yshift=-2mm,xshift=3mm},
boxed title style={sharp corners},top=3pt,bottom=2pt,
colframe=black , %<- comment by TeXnician https://tex.stackexchange.com/questions/453737/adjust-text-spacing-in-tikz-box/453741#comment1141038_453741
  title=#2,colback=white}

%%------------ Hilbert Transform ---------------

\begin{mybox}{Hilbert Transform}
\vspace*{0.5cm}
    % https://tex.stackexchange.com/questions/175969/block-diagrams-using-tikz
\tikzset{block/.style={draw, fill=white, rectangle, scale=0.9,
    minimum height=1em, minimum width=1em},
sum/.style={draw, fill=white, circle, node distance=1cm},
input/.style={coordinate},
output/.style={coordinate},
pinstyle/.style={pin edge={to-,thin,black}}}

\begin{tikzpicture}[scale=0.8, rounded corners, every node/.style={scale=1}, remember picture,overlay, auto, node distance=2cm,>=latex']
    \node [input, name=input] {};
    \node [block, right=1cm of input] (controller) {h(t)};
    \node [output, right= 1cm of controller, name=output] {};

    \draw [->] (input) -- node {$x(t)$} (controller);
    \draw [->] (controller) -- node{$\hat{x}(t)$} (output);
\end{tikzpicture}
\vspace*{0.5cm}
\end{mybox}

\end{document}