Opponents of the 24 hour day use 2 Peter 3:8 to show that the word “day” in Genesis may not mean a literal 24 hour day It reads, “But do not forget this one thing, dear friends: With the Lord a day is like a thousand years, and a thousand years are like a day.” The argument against this states that this verse is speaking of God being timeless. Additionally if this means that a day is not a day in Genesis, then a day must not be a day in the rest of Scripture.
My conclusion is that a the “days” in Genesis must be referring to a literal 24 hour day. However I also don’t see this as a salvation issue. In other words, however you interpret this, it has no impact on your eternal place in heaven or hell..