So when does the Marriage Supper of the Lamb take place in the order of events?
Right before Christ returns the great harlot and mystery Babylon will be destroyed, Rev 17, 18. The marriage supper of the Lamb follows after this with Christ returning in the air with His army of angels who are the host of heaven, Rev 19:11-14. He sends His angels out to the four corners of the earth to gather all who are dead and still alive at His coming that are His own as we are then gathered up in the clouds to meet Him in the air, Matthew 24:29-31; 1 Corinthians 15:51-57; 1 Thessalonians 4:13-18.
Once we are safely with Christ in the air, then just by Him speaking the words He takes the beast and false prophet (son of perdition) alive and cast them into the lake of fire. All those leaders from every nation on every continent that followed after the beast will be slain by the words Jesus speaks as what we read in Rev 19 is all done by Christ being in the air where we are yet with Him before He plants His feet on the Mt of Olives.
This all takes place on the last day being our seventh day of rest that has no ending for we know from that point on we will be with the Lord for ever. We can not see this as a 24 hour day as this is the time of our seventh day rest like that of God's rest in Genesis 2:3 as He sanctified that day and set it apart from all the other days, but had no evening.