First, it was one day. They would have been fine. Second, light was created before the objects meant to emit it. There was already light, just not a sun, moon or stars. And before you ask how, you know my answer will be God. I think that the universe was still an open system at this time, and that the laws of the universe hadn't yet been set in stone. The Bible says that the work of creation wasn't finished until day seven, when it says God rested, rested meaning stopped, from His work which He had done. But I have no proof for that idea. It just makes sense to me.
The heavens and the earth were created according to the laws of opposites. To have light you also need darkness. To have good, you have to have bad. To have sweet you have to have bitter. For every action there is an equal and opposite reaction. The first part was that light was added to the pre existing darkness. (Genesis 1:1-3), and the "light was called day", and "there was evening and there was morning, one day". (Genesis 1:4-5). That was the "in the beginning" (Genesis 1:1). The laws creation was built on preceded the creation. The "Word", the Law and the prophets, were from the beginning, in the form of the alpha. At the time of the omega, there will be a new heaven and earth, and it will have different laws, and will not require darkness/evil to provide bitter and sweet.