It is mentioned in the first episodes that sunshine takes place in the fifth year after Love Live inception (or the fifth tournament).
We know that in the year the first series takes place, two editions of Love Live happen (the first when they default due to Honoka's sickness and A-Rise wins, and the other when µ's wins).
So by my estimates, it should happen in the year when Alisa and Yukiho are third-years or have graduated already.
So, how long are the two series apart?
