Multiple panel figure, with figures side by side

Do you mean something like this?

In order to have figure A and B on the same line there must be no blank lines between the subfigure environments. You can adjust the distance adding a \hfill (or a \hspace{}) between them. The vertical space before figure C can be adjusted changing the value of \vspace{}.

\documentclass{article}

\usepackage{caption}
\usepackage{subcaption}
\usepackage{graphicx}

\begin{document}    
\begin{figure}
    \centering
    \begin{subfigure}[t]{0.45\textwidth}
        \centering
        \includegraphics[width=\linewidth]{example-image-a.pdf} 
        \caption{Generic} \label{fig:timing1}
    \end{subfigure}
    \hfill
    \begin{subfigure}[t]{0.45\textwidth}
        \centering
        \includegraphics[width=\linewidth]{example-image-b.pdf} 
        \caption{Competitors} \label{fig:timing2}
    \end{subfigure}

    \vspace{1cm}
    \begin{subfigure}[t]{\textwidth}
    \centering
        \includegraphics[width=\linewidth]{example-image-c.pdf} 
        \caption{Price regulation} \label{fig:timing3}
    \end{subfigure}
    \caption{Some general caption of all the figures. In (\subref{fig:timing1}) you can see a  green square....}
\end{figure}
\end{document}

Of course you can change the width of all subfigures to get three images with the same dimensions:

I obtained this new figure setting the following widths:

• figure A: width=0.5\linewidth;
• figure B: width=0.5\linewidth;
• figure C: width=0.25\linewidth;

You can adjust these values in order to obtain the desired output (or using a different command like \includegraphics[scale=]{}).

EDIT: Re-reading the question I noticed:

...and the other one below the first one...

Therefore, if you want to put figure C below A, you only need this code:

\documentclass{article}

\usepackage{caption}
\usepackage{subcaption}
\usepackage{graphicx}

\begin{document}    
\begin{figure}
    \centering
    \begin{subfigure}[t]{0.45\textwidth}
        \centering
        \includegraphics[width=0.5\linewidth]{example-image-a.pdf} 
        \caption{Generic} \label{fig:timing1}
    \end{subfigure}
    \hfill
    \begin{subfigure}[t]{0.45\textwidth}
        \centering
        \includegraphics[width=0.5\linewidth]{example-image-b.pdf} 
        \caption{Competitors} \label{fig:timing2}
    \end{subfigure}

    \vspace{1cm}
    \begin{subfigure}[t]{0.45\textwidth}
        \centering
        \includegraphics[width=0.5\linewidth]{example-image-c.pdf} 
        \caption{Price regulation} \label{fig:timing3}
    \end{subfigure}
    \hfill
    \begin{subfigure}[t]{0.45\textwidth}
        % just an empty subfigure to shift C below A
    \end{subfigure}
    \caption{Some general caption of all the figures. In (\subref{fig:timing1}) you can see a  green square....}
\end{figure}
\end{document}

that produces: