The original problem of this problem is this.

The driving time is: 18:08. Stop checking in five minutes before driving. Xiaoming needs 20 minutes from home to the railway station. In order not to miss the train, he had to leave home in the afternoon at the latest.

Answer: Depart from home at 5: 42 pm, 18: 02 to check in at the railway station. If 18: 03 stops checking in, you cannot enter the station.

I hope it helps you.