As they take data and improve their sensitivities, interferometric gravitational wave detectors will eventually detect signals emitted by inspiralling compact binary systems. Determining the sky position of the source will require that the signal be recorded in several detectors. The precision of the source direction determination will be driven by that of the time-of-flight measurements between detectors, and ultimately by the timing precision at the level of each detector. The latter is limited by the noise of the detector and the use of template banks, which introduce some mismatches between the parameters of the signal and the parameters of the template used to detect it. The standard way for signal timing is based on referring to the end time of the signal. In this paper we show that this is not an optimal choice and the timing precision can be improved referring to a time when the signal crosses some reference frequency, whose optimal value depends on the detector sensitivity.