"Please make payment by 15 Nov 2013"
Does it mean that I can make payment from now until 15 Nov 2013 11:59pm?
With phrases like that, it's a good idea to clarify. It can mean "before 15 November 2013" in which case you would have to pay by 14 November 2013, 2359 hrs. In addition, sometimes people are only referring to working hours. If you are paying a business, they might want to check that you have paid by the time they close. If their business hours are, for example, 9am to 5pm, they will check their bank account several times throughout the day to check that your money has arrived. If it's not there by 5pm on 15 November 2013, they might well assume that you have failed to fulfil your end of the bargain and you haven't paid.