You do not know
When the time
Βλέπετε, ἀγρυπνεῖτε· οὐκ οἴδατε γὰρ πότε ὁ καιρός ἐστιν
This is somewhat similar to the parable ending saying in Matthew, chapter 25:13, about the virgins at the wedding being vigilant. Mark indicated that Jesus said that they were to be aware (Βλέπετε) and alert all the time (ἀγρυπνεῖτε), because they did not know (οὐκ οἴδατε) when the end time (γὰρ πότε ὁ καιρός ἐστιν) would come. This was a simple message to be vigilant all the time because your end or the end of the world could happen at any time.