def diff_time(start_time, end_time):
    """
    Computes the elapsed time from the start time to the end time specifed by
    the user.

    Parameters
    ----------
    start_time : Datetime
        Specifies the start time of the time range to be computed.
    end_time : Datetime
        Specifies the start time of the time range to be computed.

    Returns
    -------
        time_dif : Integer
            Represents the time elapsed from the start time to the current time (when the function was called).
    """
    time_dif = int((end_time - start_time).total_seconds() * 1000)
    return time_dif
