In theory the rebellion was born in Episode II, when Bail Organa started to think that Palpatine's reign was not good for the republic. It started to take form when he gathered more senators against Palpatine and started the delegation of 1000. It depends if you consider that scene canon or not. But here the Rebellion actually already existed when they sent a team to gather the Death Star plans, so you might want to think to change the line 'A Rebellion will be born'. This takes place close to the events of A New Hope. Other than that the poster looks pretty cool. Simple, but nice and cool logo.