Considering NSBU instead of upgrade of Norton Internet Security product

I currently have Norton Internet Security with license for 3 devices and am looking at a number of options to cover additional devices, including Android mobile.  The Norton Security Backup package for 10 devices is one option that I could choose. Since I have nearly 2 months before renewal, if I upgrade now will I get credit for the time remaining?  Or should I find alternative (as in free) products for coverage in the interim?