You could easily do 50, and probably way more, but you would make it harder on yourself by spreading it out like that. The way to do it would be starting super slow (like, 2:30-3:00 per mile slower than marathon pace assuming similar terrain, so around 10:00/mile pace for you), going slower (even walking) on any substantial uphills, taking fluids regularly, and every 90 minutes to 2 hours taking a 5-20 minute break to sit, eat some real food (a banana, toast with a little peanut butter, avocado, maybe some candy like M&Ms or chocolate-coated pretzels), go to the bathroom, and change your shoes/socks/shirt, etc.
If you have your logistics squared away and make sure you address any chafing (that's what those sit breaks and shoe changes are for), overuse (don't do it around the track--or if you do, change directions every hour!), or fueling issues proactively, you can definitely do 50 miles or 100k in a day. Probably 100+, but that's where things can start getting really weird even in a controlled environment if you have any injury issues, imbalances, or don't fuel and/or hydrate properly.