"Yes, but the Apocalypse speaks of the end of times"
Yes it does, but it also speaks of things John had seen, things that were at the time and things to come. At the time of the vision it was around 95 A.D. and Jesus is saying "I [am] he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death." He is saying at the time of the vision He had the keys of life and death, physical and spiritual, which means He now exercises rule and judgment.