When does the license start for each PC on a multi PC license

Norton Security | Norton Internet Security
1

I have NIS for 3 PC's.

Have installed it on 2, no worries.

But the 3rd doesn't need it until the current security suite runs out in a few months. If I install the remaining seat then, does its 365 day license start counting down from then or from the 1st day the 1st license was used?

Thanks.