I don't think it would matter too much distance wise. They should open the IG at the same time as the main entrance, but it may not be exact, so the people at the front could get a jump or vice-versa, however there should be far fewer people at the IG meaning they will process you through faster. So, really, I don't think it matters too much. Just remember that you need to go around the west side of the WS from the IG (i.e. toward Canada), then across the plaza near Future World. If you go the other way, you can get as far as France (for breakfast) but you will not be allowed to progress further in that direction until the entire WS opens at 11 AM, so don't do that.