Preaching the Gospel to every nation would hasten the second coming.
I have to politely disagree unless you can provide a scriptural reference to verify that statement.
If God is omniscient, and He is, there can be no doubt that He knew who would be saved and who wouldn't long before He created the universe. Actually, He knew that in eternity past, which is beyond our ability to comprehend. Therefore, nothing that happens on planet Earth before Jesus Christ returns could or will take Him by surprise, including who will be the last man or woman who will accept His Son Jesus Christ as Lord and Savior and thereby complete the Body of Christ, aka His Church.