In reply to Moza:
I've been in early April. There was a massive cornice hanging over Grande Face, so avoid that. But the main sectors were fine. You'd want to be climbing in the sun, so Demi Lune etc in the morning, Cascade in the afternoon.
There was barely anyone there, so in may ways a lovely time to go. The campsite was officially closed still, but they let us on anyway.
Having said all that, I imagine slight variations in the weather could quickly make it impossible/grim. But if it does, it's only a couple of hours to St Leger.