How to subtract 2 hours from user's local time?

Subtract from another date object

var d = new Date();

d.setHours(d.getHours() - 2);

• Complete reference list for Date object

According to Javascript Date Documentation, you can easily do this way:

var twoHoursBefore = new Date();
twoHoursBefore.setHours(twoHoursBefore.getHours() - 2);

And don't worry about if hours you set will be out of 0..23 range. Date() object will update the date accordingly.