You don't need to till again. In fact tilling the first time was likely a mistake. The reason is the fluffy soil resulting from the tilling will settle differently across the area leaving you with an increasingly bumpy surface over the next 3 years. You can try now to level it some more. Check to see if the area is higher than the rest of the yard. That usually happens when you add more topsoil. You might want to remove some of that before you put the sod down. Mulching it was a great idea!

Rake back the mulch and any extra soil, remove any high spots and fill low spots. Then put the sod down and roll it to ensure you have good soil to sod contact. Well, for only 350 square feet you can just walk on it. The idea is to push down the high spots so the roots contact the soil. They will not grow through the air to reach the ground.

What kind of grass are you getting? If you are getting anything but bermuda then you don't need to fertilize until late May. If you are getting bermuda you can start fertilizing as soon as the spring flush of new growth slows down. That might be late May anyway.

Thank you, that is helpful. Let me clarify that we added topsoil because we had to remove about 5 inches of stone dust and gravel that was underneath the patio we removed. The landscaper who did the removal tilled in the new soil, and the area is overall graded level, although there is a bit of settling that we need to correct. We will be putting down tall fescue sod.

If the landscaper tilled with a tractor and not by hand and not with a bobcat, then you would have a decent shot at even settling. The problem with hand tilling is the machine bucks and jumps out of the ground when it hits a rock or root. Elsewhere it can dig in deep when it hits clay or even sandy soil. The end result is the underlying profile of the firm soil, that untilled stuff, can be very uneven. Then when it is leveled at the surface, the fluffy soil between the surface and uneven sub layer is different depths. As it settles it settles to match the underlying untilled profile. If you use a tractor with a tiller it will hold the depth very closely without bucking around or digging in. Even bobcats are too small to be reliably level.

You can also settle the soil ( and find out where the low spots are going to be) , by soaking the area over and over and over again. There,s nothing like water to show where the sink spots are going to be. After everything is "water settled", you let it dry out and do a final leveling before sod goes down.

Thank you both. No tractor was used, just a hand tiller (this is a small city yard). But it has had almost half a year now to settle, so I hope it will be ok after we do the final grading.

I think most of the settling has happened, but don't be too surprised if it continues to settle for 2 more years.