“But do not overlook this one fact, beloved, that with the Lord one day is as a thousand years, and a thousand years as one day.” 2 Peter 3:8 (ESV)
This verse has a way of bringing the heretics out of the woodwork. Harold Camping uses it as part of his method for pinpointing the day of Christ’s return and we too often see it used to support a 6000 year creation story. Yanking the verse out of context you can do a lot with it, but if we just look at the context of the verse we can understand what God has told us.
Peter is speaking about scoffers or mockers using the absense of the physpical return of Jesus as proof that His promised return was false. In response, Peter says “with the Lord one day is as a thousand years, and a thousand years as one day.” Peter’s point is that God’s time is not our time and Jesus will fulfill His promise in His own time — not ours.
Wesley is wise in saying “with God time passes neither slower nor swifter than is suitable to him and his economy.” This statement really sums up what the verse means, we should not run away with allegorizing every day into a millennium and visa versa — or worse, allegorizing the verses where it supports a point we want to make. God understands the concept of an Earth day and speaks to us accordingly.