Well it depends what kind of ninjas you have in your lineup. If you have ninjas that work in the meta and a reliable lineup, then go save for GNW. If not, build your lineups first before you save for GNW.

Anyways, there have been many people asking this right after the lighting treasure was released, and people are guessing about 3-4 months since that is the maximum amount of time we had to wait in the past for a new treasure. Keep in mind, this is only a guess and could be earlier or longer than 3-4 months.