Endowing users of multi-interface mobile handsets the competence to seamlessly roam among diverse heterogeneous wireless networks has become a crucial challenge confronting the network operators / service providers in the recent years. Today, we have moved far beyond the 3G communication networks, wherein, potential to handover traditionally relied on the channel quality computed from the received signal strength (RSS) and the accessibility of resources in new cells. These traditional handover protocols have been envisaged for the homogeneous systems possessing common routing mechanisms, signaling protocols and mobility management standards without taking users' desirable network choice into consideration. On contrary, in heterogeneous environments, mobile devices and network routers must be able to perform 'quick handovers of data sessions' amongst different networks and protocols with least possible switching delays and minimized latency, and thus regards the users' desirable network choice as significant. In this manuscript, an optimized handover decision mechanism, 'Travelling Time Prediction Based on the Consecutive RSS Measurements' in an IEEE 802.11 WLAN cell is suggested. The method uses a time threshold which is computed by a Mobile Terminal (MT) as soon as it penetrates into a WLAN boundary. The estimated travelling time is then compared with the time threshold, so as to make handover decisions for reducing the probability of handover failures. Our performance analysis reveals that the suggested mechanism effectively minimizes the number of handover failures by 60% as compared to the already proposed schemes.