Suppose you knew a loved one was going to fly into town. That much is certain. But there's a catch: you know the gate, but you don't know the date.
Say that gate has one incoming flight per day. So everyday you go to the airport, wait for the passengers to disembark, one by one, to see if that's the flight your loved one took. You never know from one day to the next, or week, or month, when they'll arrive, yet you know they're scheduled to fly into town, and you know where to find them when that happens.
You will keep on going back to the airport until they arrive. You will cease going back to the airport once they arrive.
That's rather like what the Bible says about the return of Jesus. It calls for a degree of preparedness.