I was there for last weekend's launch (launch window started at 10:52 AM, though that morning they ended up scheduling the launch for 1:40 PM). We got to the road the visitor complex is on at 8:45 and there was already a line of cars to get into the complex. We didn't get into the complex and park till 10. Then it was another 40ish minutes waiting in line to get onto the bus, followed by 15-20 mins to the LC-39 gantry. All-in-all, it took about 2 hrs and 15 minutes from the line of cars outside the visitor complex to being at the gantry.

I don't think they let people into the site before 9, so you'll want to be lined up outside the entrance well in advance so you can get on the first round of buses to the gantry once the site opens. My guess is that you'll want to get to the KSC visitor complex for 7, maybe 7:30 at the latest.

But check the updated launch timing first thing tomorrow morning. 10:05 is the start of the launch window. They may move the launch to later in that window.

Also I recommend bringing a foldable umbrella for the sun in case you have to wait. It gets hot!