How available are walk-in sites during the summer months on the weekends? (Saturday night stay) Do I need to get there at 5am or if I roll in around 10am will I still be able to get a spot?

We walked in a few weeks ago for Saturday night stay and were able to find a spot in the afternoon. YMMV

We went for our first time at the end of June (Friday through Sunday). They're probably were one or two spots available at 10:00 a.m. The're also is a campsite across the street.

I was there this Friday 8/9/2019 and I arrived at 5 pm. There were still 8 walk-in campsites available. I got a nice secluded spot. There is no need to rush there.

You should have a good chance getting a spot as long as you don't arrive in the afternoon. I did a walk-in site when I visited here and I arrived at 1130 and found a spot pretty quickly. The walk-ins were all gone by about 2 if I remember correctly.