That depends on a few factors. How far are you planning on hiking in the Devil’s Garden? Devils Garden can be a short hike to landscape arch or double-o arch or an 8 mile loop hike along the primitive loop which will take you by both of the arches, but also much more into the backcountry. If you choose to do the 8 mile loop, you might not have much energy left to do anything else except get into your hotel hot tub! If you only choose to explore only the most popular area of Devil’s Garden you could be done in 2-3 hours and then you could still do the Fiery Furnace in the afternoon.
Now, if you’re hiking in Moab in the middle of the summer you will quickly realize that afternoons are best for a long siesta in the shade of a cottonwood tree, on a sandy beach of the Colorado river, and not hiking. But if you are super determined, the Fiery Furnace due to its nature is largely in the shade most of the day so it could be done in the afternoon as long as you bring lots of water and take lots of breaks. Even though it’s only 2 miles, it will feel like exercise because you will be doing a lot of climbing and maneuvering which will wear you out.
So, it’s possible to do both, but why? Why not just add another day to your Moab visit and really enjoy these two places the way they should be enjoyed – deliberately and in-depth!
