Virtually all the sources I've read, from various persuasions, say the word translated "day" can mean only "day" in the given context. (Evenings and mornings, specifically numbered days, etc.) Thus, that seems most likely to be the intended meaning. But it's certainly possible we're reading it more literally than the Author intended.

Grishny asked if there was more importance to the question of six days/umpteen billion years. Deep time presents no challenges to Christian theology that I know of until about twelve billion years into it, when we run into That Other Debate about the origin of life, which has all-or-nothing consequences. Death before sin would make salvation a sham.

As Nyperold noted, the story does leave room for events of less interest to the human author between verses 1 and 2, and also between 2 and 3:

1 In the beginning God created the heavens and the earth.
2 Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.
3 And God said, "Let there be light," [ . . . ] the first day.

It sure doesn't sound like the heavens and the earth were created on the first day, but I'm no expert in textual criticism. Perhaps time before light wouldn't count as a day. One can't know for sure yet. My own view is that the autographs of the creation story are entirely correct, and our present copies have all doctrinally important details correct as well.

gabby