Add time to date field

Add time to date field

I have a date field that I am wanting to take upon user update and add the time to it and put that into a date time field. I keep getting an error when I try this:
    date = input.runDate + " " + zoho.currenttime.toString();
    input.startTime = date.toTime();
    input.endTime = input.startTime.addHour(1);

It gives me the error unable to convert string to date. What is a better way to accomplish this?