Returns a new CalculationDate on the specified date and optionally time. If the time is not supplied in the input it will default to 00:00:00. 

var date = now.valueOf('2017-03-15'); 

console.log('date = %s', date);

//date = 2017-03-15 00:00:00

date = now.valueOf('2017-03-15 23:59:59');

console.log('date = %s', date);

//date = 2017-03-15 23:59:59
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