JR already handled this quite well and so I won't go into detail here except to say that there isn't anything the slightest bit irrational about 2 Peter 3:8.There is nothing rational to the natural mind that the statement that a thousand years are equal to one day in God's eyes while at the same time, one day is equal to a thousand years in God's eyes. The natural mind cannot explain that in secularist mathematical terms.
The verse isn't try to tell you that a thousand years IS a day to God and and that a day IS a thousand years. It's an expression with a completely obvious meaning. It's just saying that God doesn't care how long it takes. It's not as if God is going to run out of time and He's as perfectly patient as His perfect wisdom requires Him to be. In short, God isn't worried about how long something takes to happen. Whether it takes a single day or 365243 days (i.e. a thousand years) it makes no difference to God.
I will also take this opportunity to emphasize an important point that I've made repeatedly over the years...
There is no such thing as an irrational truth. If some claim is irrational, it is false - by definition. If you discover some aspect of your belief system that proves to be irrational then you have discovered an aspect of your belief system that is false and you have a choice to make. You can reject the belief as false or you can choose to believe a lie. There is no third option. It's reject the falsehood or lie to yourself. There is no in-between. In any compromise with sound reason, only falsehoods can profit.