You have this backwards. It is better to pay in installments due to the time value of money since there is no interest. You want to be the one holding onto the money, so if you can delay giving it away, that's where you get the time-value of money.
If you pay $120 at once, that's $120 completely gone with no time-value gained.
If you pay $10 per month, you get to keep $110 the first month to invest. Month 2, you have $100 left plus what you earned last month to invest. At the end of 12 months, you'll have spent the same $120, but you gained money either by investing it or at least gaining interest.