Calculation of daily traffic on a 3G-modem.

Please tell me a program for Windows XP / 7 for traffic accounting when connecting to the Internet via a 3G modem. It is the division of traffic day / night that interests, at night it is free, and the daytime is limited to 30GB, often there is a problem of overspending the daily limit. now I have DU Meter, an excellent program, but one drawback - it shows the total volume, but I need to divide it. In general, help with the choice of pzhlst)))