\documentclass[letter]{article}
%\input \jobname

\def \dayOfWeek{Week 9}
\def \date{2019/10/21-23}
\def \colwidth{56mm}

\usepackage[utf8]{inputenc}
\usepackage[letterpaper, margin=1cm]{geometry}
\usepackage{array}
\usepackage{graphicx}
\usepackage{colortbl}
\usepackage[x11names]{xcolor}

\pagenumbering{gobble}

\renewcommand{\arraystretch}{1.6}

\newcolumntype{C}[1]{>{\centering\arraybackslash}p{#1}}
\newcolumntype{M}[1]{>{\centering\arraybackslash}m{#1}}
\newcolumntype{S}{>{\centering\arraybackslash} m{.4\linewidth} }

\definecolor{anti-flashwhite}{rgb}{0.95, 0.95, 0.96}

\newcommand*{\grayline}{%
	\arrayrulecolor{anti-flashwhite}
	\cline{1-3}
	\arrayrulecolor{black}
}

% TODO: Make this reactive
\newcommand\textbox[1]{%
	\parbox{60.5mm}{#1}%
}

\begin{document}
\centering

\begin{tabular}{ |r|r|p{35mm}|p{48mm}| }
		\hline
		\multicolumn{4}{|c|}{ 
			\cellcolor{anti-flashwhite}
			\noindent
				\textbox{\date \hfill}
				\textbox{\hfil Semester Planner \hfil}
				\textbox{\hfill \dayOfWeek}
		}\\
		\hline
\end{tabular}

\begin{tabular}{|m{1em}|m{\colwidth}|m{\colwidth}|m{\colwidth}|@{}m{0cm}@{}}\hline
   & \centering Monday & \centering Wednesday & \centering\arraybackslash{Other} \\\hline
   \centering\rotatebox{90}{C311} &&& \\[75mm] \hline
   \centering\rotatebox{90}{C346} &&& \\[75mm] \hline
   \centering\rotatebox{90}{C490} &&& \\[75mm] \hline
\end{tabular}

%\begin{tabular}{ |m{11mm}|C{54mm}|C{54mm}|C{54mm}| }
%	\hline
%	Course & Monday & Wednesday & Other \\\hline
%	\rule{0pt}{78mm}C311 &&&\\\hline
%	\rule{0pt}{78mm}C346 &&&\\\hline
%	\rule{0pt}{78mm}C490 &&&\\\hline
%
%\end{tabular}

\end{document}