Various Theories Concerning Genesis 1

• Day–Age: After each lit­er­al 24-hour days of Cre­ation (all six of them), Yah­weh per­mit­ted a great time to pass — which com­prise the geo­log­ic ages of Earth — in order to allow His cre­ations to mature & devel­op gradually.
• Gap: Gen­e­sis 1:1 describes an orig­i­nal cre­ative event which sub­se­quent­ly fell into ruin as a result of some kind of dis­as­ter, often believed to be Satan’s rebel­lion. An unknown amount of time — a gap — exists between Gen­e­sis 1:1 & 1:2, and the six days of Cre­ation are in effect a recreation.
• Indef­i­nite Age: The six days of Cre­ation are not lit­er­al days but are of inde­ter­mi­nate length, allow­ing for a res­o­lu­tion of the the­o­ry of evo­lu­tion, geo­log­ic ages, and the Gen­e­sis 1 record. The order of the days is not important.
• Sev­en Day: The six days of Cre­ation are six true days with­in which Yah­weh cre­at­ed the heav­ens, the earth, and all that in them is. This Cre­ation took place an inde­ter­mi­nate amount of time ago.
• Rev­e­la­to­ry Day: The sev­en days of Gen­e­sis 1 are not sev­en days in which Yah­weh was cre­at­ing & rest­ing; rather, the sev­en days are the week in which Yah­weh revealed to Moses the events of Cre­ation, which tran­spired over the course of an unknown length of time in the unknow­able past.
• Rev­e­la­to­ry Device: The sev­en days are noth­ing more than a lit­er­ary device used by the author of Gen­e­sis in order to bet­ter orga­nize & present his thoughts.

Source: Baf­fling Bible Ques­tions Answered by Lar­ry Richards, page 18.

I per­son­al­ly believe that only one of those the­o­ries — Sev­en Day — plays nice­ly with the whole of the Scrip­tures, par­tic­u­lar­ly Exo­dus 20:8 – 11. How­ev­er, as Lar­ry Richards says on page 19:

Spec­u­la­tion and argu­ment are always of inter­est. But this is one ques­tion that will not, and need not, be resolved. For the issue is not how God went about cre­ation but that God did cre­ate. It is not nec­es­sary that we know how he did this. It is nec­es­sary that we affirm the fact that he did it. Every­thing in the mate­r­i­al and spir­i­tu­al world exists because God called it into being. This is the unshak­able bedrock of Scrip­ture’s vision of reality.