I'm not sure when they open the lot. I'd guess 10 AM. There is really only one way to enter the Simba lot as of right now. If you're coming from the 5 South, just take the Disneyland Drive exit like you would to get to the parking structures and continue straight down towards the Paradise Pier Hotel. From there they will guide you in to the parking lot. If you try to enter from the Katella side, there will be cones not allowing you to make a left or u-turn and you will have to go all the way down Disneyland Drive and then make a u-turn at Ball, so avoid the hassle.
Keep in mind that they "pause" parking throughout the day. There are times where you won't be able to get in for a bit but if you are there early I'd imagine it's fine.