First-flush tea shipped as soon as it is picked. The appeal is the fresh, green aroma, and it is usually given a lighter final firing to preserve it. Since that aroma settles with time, shincha is really a state of the tea rather than a separate type.
In more detail
Shincha and ichibancha describe the same tea from different angles: ichibancha is the grower's word for the first picking, shincha the seller's word for tea shipped fresh. It is usually fired lightly to preserve the green aroma, which also means it does not keep. Buy it to drink now.