The context of this verse is in connection to the Second Coming of Christ. Peter is recognizing the impatience of some believers who just wish "He would come NOW!" Peter is also sensing the sarcasm of unbelievers who ridicule Christians for their belief that "Christ is coming back" and he was thinking, "they've been saying that for the last 30 or more years!" And that's how they were thinking in the first century! No wonder people are still mocking today! But Peter wanted believers, and even unbelievers to understand that God moves in His own time and has reasons for waiting - we'll look at verse 9 later.
What strikes me about "a day is like a thousand years..." is that God is capable of doing a thousand years' worth of work in one day! Have you ever had one of those remarkable days when you felt you accomplished so much in a few hours when you've had days when hardly anything gets done? What's the difference? May I suggest instead of laziness you started your day with a meaningful time with the Lord. Your quick "saying grace" at breakfast became a "sweet hour of prayer!" Prayerlessness and unproductivity go hand-in-hand. God is ready to do a lot when we are ready to pray a lot! Try it.
Second, the last part of the verse says "a thousand years is like a day." God can move very rapidly when and if He wants to! His timetable is His and He doesn't move when we think He should. This is a good thought to remind us to plan ahead for a hundred years with the thought we could have at least that much time to do more to fulfill His Great Commission. Of course, in our planning we should always be mindful He could suddenly say, "That's it!" We don't know when, but we don't need to know. He knows and that's satisfying to me.