WiFi Hotspot GoPhone plan

I'd like to understand the WiFi Hotspot GoPhone plan.      I have a summer camp where I would use it once or twice a year where there is good ATT coverage.     Can I activate for a month, and then have it dormant for the rest of the year and then pay the monthly fee only when I need it again?      

The Amazon listing shows "  Convenient and flexible - Renew your service when you need it for up to one year after your plan expires "    So my understanding is that I could use this for 1 month each year by adding the credit for one month.     There is also info on the GoPhone site that shows a 60-day period where you would need to buy a new SIM card, so it is confusing.   Is it 365-day period or 60-day period?