I've been wanting to do this too! I think one of the major factors to consider when deciding to do it is where you are. A few years ago, my dad converted a stretch of lawn similar to the size you want to do into a meadow, just around where my sister situated her honeybees. My parents are in a very rural place where wildflowers grow like mad all around them, so it didn't take too long. He cut the grass a few times in the spring, and then just let it grow and then scythed it to the ground before the next spring. And he did this for several years--there are so many different types growing in the area now, it's a bonanza for the bees. If you're in a more developed area, it may take a little longer for a variety of flowers to get naturally seeded.
I'm not quite as rural as my parents. I'm going to try and stretch of about 20' x 50' this year and follow this "recipe":
https://www.meadowsandmore.com/wild-gardens/making-a-meadow/ . It may take a while, but I'll try it and see what happens :)