1\section{Temporal variation}2\label{sec:temporal}34The relevant clock for an implicit price is the period of the transactions, not the year of publication, and the two differ by a5median of several years in the extracted studies. Figure~\ref{fig:temporal} plots the harmonised estimates of the six most-studied6combinations against the midpoint of the transaction period, with a precision-weighted trend, and Figure~\ref{fig:density} gives7the density of evidence by characteristic and decade. The pre-2000 evidence is thin in the extracted sample, which is dominated by8transactions from the 2000s and 2010s and, through listing data, the 2020s. Within that window the trends are small relative to9the dispersion: the living-area elasticity is flat, the age semi-elasticity drifts toward zero, and the bathroom and bedroom10semi-elasticities decline, consistent with the increasing inclusion of area controls in later specifications rather than with a11change in preferences. In the moderator models, the data-period variable is significant in \nSigPeriod{} of \nTestedPeriod{}12specifications. The pre-registered hypothesis of rising premiums for energy efficiency and green space after 2008 cannot be tested13with power: both families have fewer than fifteen studies and their estimates are dominated by specification differences. The14same is true of the financial crisis and of the COVID-19 pandemic, for which the extracted studies are few and their designs15heterogeneous; the paper reports no pooled pre/post contrast for them.1617\begin{figure}[H]18\centering19\includegraphics[width=\textwidth]{fig09_temporal_evolution.pdf}20\caption{Harmonised estimates against the midpoint of the transaction period, with a precision-weighted linear trend (marker size21proportional to precision).}22\label{fig:temporal}23\end{figure}2425\begin{figure}[H]26\centering27\includegraphics[width=0.85\textwidth]{fig12_evidence_density.pdf}28\caption{Evidence-density matrix: number of extracted studies by characteristic and decade of the transaction data.}29\label{fig:density}30\end{figure}31