It opens at the same time as the main entrance. Most days you can enter and walk as far as the bridge between England and France. There is a rope and a couple of CMs there who let you in when the park opens for the day.
In my experience, it takes about the same amount of time to get to Soarin' from the IG as it does from the main entrance, perhaps a shade longer. We have been able to get a FP, wait a short time in the standby line to ride and then ride almost immediately again using our FPs. By the time we were done with the second ride, the standby line was 45 minutes or more.