In my opinion, it is not really accurate to compare the placenta to a grocery-bought piece of raw meat. Raw steaks that you see in the stores have traveled to get there and are not fresh off the cow (they may even be a couple days old). Your placenta will be literally brand new from your body. Depending on the temperature in your house, it may be appropriate to leave baby attached for a couple hours or more. Go with your gut feeling. You will know when it is time to detach baby from the placenta.
As far as size and practicalities, anticipate the placenta being about the size of a dinner plate and around an inch in thickness. You will need a colander to go inside a big bowl to allow your placenta to drain (and drain it will!). When you are ready to separate it from your baby, do so in whatever way you choose, and then have your appointed placenta preparation person bring the colander and bowl to the sink and rinse it (and rinse it and rinse it and rinse it...you'd be amazed at how much you must rinse it before the water runs almost clear). I recommend rinsing thoroughly for smoothie consumption...it's not as necessary for encapsulation because you will not taste any blood in the capsules.
Anyway, when it is good and rinsed, use a very sharp knife (preferably filet--placentas are TOUGH) to cut off any dangling membranes and the umbilical cord, and then cut the placenta into 1-2 inch chunks. You can then place these chunks on a plate (keeping space between them so they don't touch each other), and place the whole plate in a large zip-lock freezer bag. Then put the whole thing in the freezer and use one piece at a time for your smoothies (the first smoothie can be made right after your baby's birth with a raw, unfrozen piece of placenta!). This is my preferred method. Some mamas put the placenta chunks in the fridge for a couple days before transferring to the freezer. I don't like to take the chance that any placenta will get funky.
Hope this helps!