Let’s read Genesis 1:1-8, “In the beginning God created the heaven and the earth. And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters. And God said, Let there be light: and there was light. And God saw the light, that IT WAS GOOD: and God divided the light from the darkness. And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day. And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so. And God called the firmament Heaven. And the evening and the morning were the second day.”  Now, let’s read verses 9-10, “And God said, Let the waters under the heaven be gathered together unto one place, and let the dry land appear: and it was so. And God called the dry land Earth; and the gathering together of the waters called he Seas: and God saw that IT WAS GOOD.”  I encourage you to read Genesis 1:12, 18, 21, and 31.

Reading these, we see that you are right.  After the 2nd day of creation, the Lord did not declare it to be good, while for all the other five days of creation, the Lord saw that the creation of each day was good.  Why is this? 

Before looking at your question specifically, it would be good to read Genesis 1:31, “And God saw every thing that he had made, and, behold, IT WAS VERY GOOD. And the evening and the morning were the sixth day.”  This shows us that the Lord was pleased with all His creation and declared it to be VERY GOOD.

Some have proposed that the Lord did not actually ‘create’ anything on the 2nd day, He simply separated what He had already created on the first day.  Again, verse 6 tells us, “And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.”  The word ‘firmament’ can be a little confusing.  A firmament is actually an expanse, so on the 2nd day, the Lord separated the earth from the clouds, thus exposing the atmosphere to us. 

Others have proposed that if God did actively create something on the 2nd day, He may have spent his creative time on the heavens, so this would have been the only day where earth was not the primary focus of his creation.

Your thought of the Lord not declaring the 2nd day good because of Satan being “the prince of the power of the air” as brought out in Ephesians 2:2 cannot be rejected.  That thought seems to be as feasible as the other two thoughts.

If we continue reading in Genesis, we will see the Lord did not declare the 7th day to be good.  We read in Genesis 2:1-3, “Thus the heavens and the earth were finished, and all the host of them. And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made. And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made.”  Perhaps it was because He did not create anything on the 7th day that the Lord did not declare it to be good.  This would give credence to the thought that He did not declare the 2nd day good because He did not actually create anything on it. 

Before closing, I think it is good to point out that after His act of creation, the Lord declared one thing as NOT GOOD.  Genesis 2:18 says, “And the LORD God said, IT IS NOT GOOD that the man should be alone; I will make him an help meet for him.”  God in His infinite wisdom and love knew that man was not complete without woman, so He made Eve by taking a rib from Adam’s side.  We read in Genesis 2:21-23, “And the LORD God caused a deep sleep to fall upon Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof; And the rib, which the LORD God had taken from man, made he a woman, and brought her unto the man. And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man.”  It was at this point, the Lord instituted marriage as we read in verse 24, “Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.”  Even before there ever was a mother and father, the Lord established marriage and its proper order.  (CC)  (585.4)