No advantage to using the train, which won't start until 10am when IoA "opens."
If you enter IoA you will be able to get into Seuss Landing during early entry hours - anyone can enter the park, they check your EE status on the way into Hogsmeade Harry Potter area (actually, the separation starts much sooner, but there are adjacent paths through Seuss area, and non-EE is blocked from going past Seuss).
You could explore Seuss scenery for a bit and hang out near the barricade as 10am approaches. The Hagrids line does drop a bit as EE hour continues, but then balloons back up as soon as regular hours start again. So you could aim to be at the Seuss barricade as early as you'd like to be at the start of the second "rope drop" of actual opening at 10am.
That being said, if the parks are not that busy then you can get on Hagrids with reasonable waits through much of the afternoon (30-50min). Mornings are busiest, except EE rope drop. I'd say that weekday afternoons were consistently shorter waits during my trip than the morning, except when weather or technical issues caused significant delays during the morning. We rode for the first time on a Tues afternoon and got in line around 4:30 with about a 45min total wait.
When you get past the locker clusterf, the wait is about 40min if the whole queue is in use. So if the line to the lockers has a visible end from the train station, it should be 45min or so.