There is never a totally safe age or size to free range whether they are bantam or full sized. Even if they were full grown turkeys dogs, coyotes, foxes, bobcats, and others pose a threat in the middle of the day. A bird of prey can take a bird larger than itself, it can't carry it away but eats it on the spot. Size does matter to a snake, it depends on the size of the snake and the chicken. You probably don't have any snakes in Maryland big enough to take your 12 week old bantams. Any time you free range you take a risk. I agree, at 12 weeks they are as ready as they will ever be.
You'll get different opinions on the danger of free ranging because we all have different experiences. I grew up in the middle of the ridges of Appalachia, my parents totally free ranged, no chicken fences at all. Some chickens slept in trees. All the time I was growing up we had a total of two predator attacks, a dog and a fox. We had owls and hawks, as far as I know we never lost a chicken to any of them. Averaging one attack every nine years wasn't bad. Both the dog and the fox were shot.
I tried free ranging when I retired and moved here. I lost two chickens the first three years, probably to a fox or coyote. I wasn't happy but I didn't consider it horrible. Then I had attacks by dogs. The first two dogs took out eight chickens before I shot them. The second attack was five lost to one dog while I was off visiting my granddaughter. The chicken watcher left them locked up until I got back and I got electric netting to stop dog attacks. That ended my free ranging, the problem is that this is a great place for people to abandon dogs in the country. All those losses were adults or mostly grown juvenile chickens.
I raise a lot of baby chicks. I have lost a few of those to snakes over the years, but very few.
I have owls at night and lots of hawks around during the day, mostly red tailed hawks. Over the years I've lost a total of two chickens to birds of prey, one each hawk and owl. The owl was my fault, I didn't lock them up at night early enough. Some people have a huge problems with birds of prey, some don't. Some of that depends on what exactly your birds of prey are. Cooper's hawks are smaller than red tailed but are more likely to go after a chicken.
The bottom line is that no one can tell you what will happen to your chickens if you try to free range. You may go many years without any problems at all, you may be wiped out the first day you try it. This stuff does not come with guarantees.
You often see on here that certain predators only attack at night. That is not true, practically any predator can be hunting during the day. I even saw an opossum feeding at my compost pile at 1:00 in the middle of a sunny afternoon. I'll admit that surprised me. For different reasons your threat is much greater at night. Many are more active at night and since you are in bed, they have a lot more undisturbed time to do their mischief. However you decide to manage your chickens I strongly urge you to lock them in a secure coop after dark.
I don't know what your property looks like or what you mean by free ranging. For some people free range means no fences, for some people allowing them to forage in a limited area at limited times count. It sounds like your risk tolerance for losing one isn't very high. I fully understand that. The best way to protect your chickens is to use barriers. What kind of barriers depends on what predators you are protecting against, how much money you want to spend, what your terrain looks like, how big it is, and how cute you want it to look. Some people build very small covered runs and try hard to make them absolutely predator proof. I opted for electric netting around a large are so they can forage for some of their food but they are vulnerable to birds of prey, which hasn't been a big problem for me. Others do other things with varying degrees of success.
I don't know what the right answer for you I as far as how you protect them but at 12 weeks they are ready to do their part.
