One thing that has always bothered me about Creation apologetics is that I very rarely see 2 Peter 3:5-6 as a refutation of misquotes of 2 Peter 3:8. Being part of the same passage, I would imagine this should be easy. The people using 2 Peter 3:8 as evidence against a literal understanding of Genesis are literally fulfilling 2 Peter 3:5-6 by arguing against a literal understanding of Genesis!
Now, that's not to say that creation ministries fail in their response. They always put verse 8 back into context by pointing out that it isn't saying God is somehow incapable of telling us how long He took to create the heavens and the earth; He is saying that just because He seems to us to be taking too long to return does not mean He actually is; He's taking His time for the sake of those who may repent in the future. That isn't a bad answer, it's actually a very good answer.
But it could be better. We don't just need to show Old Earth Creationists the real context behind the verse they're misquoting, we need to demonstrate their hypocrisy in misquoting it. The fact that backing up just 4 verses not only shows the exact opposite of the case they are trying to make, but also reveals the very motive so many people have for making that case, indicates that those who do make that case are severely lacking in their walk with God. Their sources are deficient, their studies are slack, and their faith is weak. Anyone who claims that 2 Peter 3:8 shows that God might not have meant 6 days when He said 6 days has not sat down and honestly read 2 Peter. They may have sat down and read Hugh Ross. They may have sat down and listened to William Lane Craig. They have not sat down and read what the Holy Spirit directed Peter to say about the very thing they are debating.
Praise be to God, there is a cure for this sloppy theology. The cure is to lay our heresies at the foot of the cross and prayerfully consider the words of the scriptures. Let no man say that God has not been gracious: Every theological error, from Old Earth Creationism to full blown idolatry, can be repented of, forgiven, and corrected by the scriptures, which are now more readily available to us than ever before. Much blood was spilled to make this so. Faithful men were brutally martyred just so we could have it in English. Now we have it in every major language, and it can even be accessed online! There is no excuse; study the word (2 Timothy 2:15) or cease to speak on it (Psalm 50:16-17).