Not only will you be able to get a selected amount of NES/SNES games every month that will have ONLINE play. But, they are clarifying now that you can play these games at any time you like as long as you have an active nintendo subscription.
You will not be restricted to playing only during that month. Its like Playstation Plus where as long as you are subscribed you can play the selected games.
Which means I would recommended jumping from the start so you can take advantage to all the games that come out.
The prices of Nintendo membership starts at $3.99 for 1 month access, $7.99 for 3 months and $19.99 for 1 year access.