We consider a linear Schrödinger equation, on a bounded interval, with bilinear control.In [10], Beauchard and Laurent prove that, under an appropriate non degeneracy assumption, this system is controllable, locally around the ground state, in arbitrary time. In [18], Coron proves that a positive minimal time is required for this controllability result, on a particular degenerate example.In this article, we propose a general context for the local controllability to hold in large time, but not in small time. The existence of a positive minimal time is closely related to the behaviour of the second order term, in the power series expansion of the solution.Theorem 2 There exists ǫ > 0 such that, for every d = 0 and u ∈ L 2 ((0, ǫ), R) satisfying |u(t)| < ǫ, ∀t ∈ (0, ǫ), the solution (ψ, s, d) ∈ C 0 ([0, ǫ], H 1 0 ((0, 1), C)) × C 0 ([0, ǫ], R) × C 1 ([0, ǫ], R) of (1.9) such that (ψ, s, d)(0) = (ψ 1 (0), 0, 0) satisfies (ψ, s, d)(ǫ) = (ψ 1 (ǫ), 0, d).The goal of this article is to go further in this analysis:1. we propose a general context for the minimal time to be positive (in particular, the variables s and d are not required anymore in the state), 2. we propose a sufficient condition for the local controllability to hold in large time; this assumption is compatible with the previous context and weaker than (1.7), 3. we work in an optimal functional frame, for instance, our non controllability result requires u small in L 2 -norm, not in L ∞ -norm as in Theorem 2, 4. we perform a first step toward the characterization of the minimal time.