function getTimeOffset(string) {
    return (((+string.substring(0, 2)) + 21) % 24 * 60 + (+string.substring(3, 5))) * 60000;
}
Return a time offset based on a time expression.
@param {string} string - Time expression in "hh:mm" format
@returns {number} The number of milliseconds elapsed since the last 3am