This paper examines the interday and intraday dynamics of the euro area overnight money market on the basis of an original set of market activity and liquidity proxies constructed from both pre- and post-trade data. The empirical literature provides extensive evidence supporting the rejection of the martingale hypothesis both between days and within days, primarily for interest rates and volatility. We extend this analysis and investigate the seasonality of market activity and liquidity in a market dominated by utilitarian traders. We provide evidence that the Eurosystem's operational framework and calendar effects cause the observed regular patterns. We additionally show that utilitarian trading intensifies at the turn of the reserve maintenance period. The increased uncertainty associated with greater information asymmetry between market participants when reserve requirements become binding lead to a deterioration of market liquidity. Our analysis additionally turns out to be sensitive to the implementation in March 2004 of structural changes to the operational framework and to the more frequent occurrence of fine-tuning operations since October 2004.