Given it's a busy time of year (spring on a weekend), there's little difference between Friday 8pm and Saturday morning IMHO. By 8pm, the sites that are empty will probably still be empty early the next morning.
The one thing I will say (and you didn't say what your requested loop # was or what type of site you have reserved) is that if you come in on Saturday morning, if you DON'T get a site in the loop that you want, you have the option to say that you will wait for one to come open if somebody is checking out the same morning you come in. Whatever your plans are for the check-in day, it comes down to how bad do you want your requested loop? That's along the lines of what Scott posted. On a Friday night you have to choose from what's available. Period.
For example, kfam, say you want loop 1400. You might come in Saturday morning at 9am and there are no empty spots at 9am and the CM has you in 500. You can ask (no guarantee) to wait for someone who MIGHT be checking out of 1400 that same morning and ask that it be assigned to you. Let's say me/Ed was coming in and I specified on my early check-in option on
MDE that I would arrive at 5pm and I was pre-assigned a site in 1400. The CM would likely take my site and give it to you (although you would have to wait till it was cleaned and prepped). I might be given your pre-assigned site in 500 (and wouldn't have any idea what happened). You'll do the check-in process with the CM and they will likely take your cell number and text you the site number when it's ready. Then you just drive in, head to your loop, and set up.
Now if you have something major scheduled for Saturday there might be a conflict. But if you check in during the morning, you can let events unfold and if things didn't work out for you initially, then you can give them another chance that morning at the last minute. I can't say things will work out for you (it might be fine from the get-go). But as I say, if you have some flexibility, give yourself every opportunity to get into your requested loop.
My 2 cents. Worth what you paid for it. Hope you check in with us regardless when you get to the Fort and tell us the weather is fabulous!
Bama Ed