While I have no formal training in Greek, the moment I saw your question I remembered that this was covered in this excellent series, "Daily Dose of Greek" (http://dailydoseofgreek.com). It is a 3 minute video (most are) and it explains the function of the perfect. The relevant bit is at about :40 (forty seconds in):
However, like ALL of the scriptures, Revelation is a historical artifact now. The Torah, the prophets, the gospels, all the letters by the apostles (other than Paul) and all of Paul's letters except Ephesians and Colossians (I don't consider the addressees of these letters original) are written to saints in this age. The rest were other people's mail. We are not in their situation.
Can we learn from the historical books? Of course. They are background and examples: "shadows" and types.
John is alluding to this passage and the point is that Jesus is paying a surprise visit to his servants. If they are anticipating his arrival (though they don't know the day or hour) then he will reward them by feeding THEM. If not, they are lousy employees and he'll whack them upside the head:
Luk 12:35-48 NASB - 35 "Be dressed in readiness, and keep your lamps lit. 36 "Be like men who are waiting for their master when he returns from the wedding feast, so that they may immediately open the door to him when he comes and knocks. 37 "Blessed are those slaves whom the master will find on the alert when he comes; truly I say to you, that he will gird himself to serve, and have them recline at the table, and will come up and wait on them. 38 "Whether he comes in the second watch, or even in the third, and finds them so, blessed are those slaves. 39 "But be sure of this, that if the head of the house had known at what hour the thief was coming, he would not have allowed his house to be broken into. 40 "You too, be ready; for the Son of Man is coming at an hour that you do not expect." 41 Peter said, "Lord, are You addressing this parable to us, or to everyone else as well?" 42 And the Lord said, "Who then is the faithful and sensible steward, whom his master will put in charge of his servants, to give them their rations at the proper time? 43 "Blessed is that slave whom his master finds so doing when he comes. 44 "Truly I say to you that he will put him in charge of all his possessions. 45 "But if that slave says in his heart, 'My master will be a long time in coming,' and begins to beat the slaves, both men and women, and to eat and drink and get drunk; 46 the master of that slave will come on a day when he does not expect him and at an hour he does not know, and will cut him in pieces, and assign him a place with the unbelievers. 47 "And that slave who knew his master's will and did not get ready or act in accord with his will, will receive many lashes, 48 but the one who did not know it, and committed deeds worthy of a flogging, will receive but few. From everyone who has been given much, much will be required; and to whom they entrusted much, of him they will ask all the more.
This passage seems to allude to the generation to whom Noah preached, who ignored him and were swept away in the flood:
Luk 13:25 NKJV - 25 "When once the Master of the house has risen up and shut the door, and you begin to stand outside and knock at the door, saying, 'Lord, Lord, open for us,' and He will answer and say to you, 'I do not know you, where you are from,'
Gen 7:15-16 NKJV - 15 And they went into the ark to Noah, two by two, of all flesh in which is the breath of life. 16 So those that entered, male and female of all flesh, went in as God had commanded him; and the LORD shut him in.
When the LORD (IE: the Christ coming in his Father's name) knocks it is not wise to delay responding or to be prepared for his arrival.