"Ach, Du liebe Zeit" means nothing, it's just like "Oh, my God". Word for word translated it would mean: "Oh, you lovely time". Which makes no sense. It's an rather old fashioned saying to express beeing surprised. In this case from the sudden recall of some facts from the past. Could also be translated as "Oh, what crazy times".
The latter means "Now I remember myself again." Sounds not well but helps to understand. You find "I" and "myself". Better translated would be:
"Oh, my God! Now I remember"