Step 1: Heat conduction in a homogeneous solid (copper) depends primarily on:
\begin{itemize}
\item Shortest conduction path,
\item Cross-sectional area available for heat flow,
\item Absence of bottlenecks or constrictions.
\end{itemize}
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Step 2: Since heat losses are neglected, the point that will reach the source temperature earliest is the one with the least thermal resistance between it and point \(P\).
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Step 3: Examine the geometry:
\begin{itemize}
\item Points A and B lie across a narrower section with reduced cross-sectional area, slowing heat flow.
\item Point D is farther from \(P\) along a longer and thicker path.
\item Point C lies closest to \(P\) through the most direct path with comparatively larger conducting area.
\end{itemize}
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Step 4: Hence, heat reaches point C earlier than the other points.
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Final Answer:
\[
\boxed{C}
\]
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