We believe Jesus is coming soon. But, how soon is "soon?"

"Soon" can have a relative meaning. How should we understand it in this day and hour? And while we're on it, have the last days already begun? If so, when? Did Peter the Apostle leave us a crucial clue when he wrote, "Beloved, do not forget this one thing, that with the Lord one Day is as a thousands years, and a thousand years as one Day"?