I'm currently in chapter 229 of the manga and it keeps referencing Hayate traveling in time to when Nagi still lived in Mykonos with her mom and he ended up saving her but i don't reading that could someone tell me the chapters that story takes place. 1e5ge

Also what happened to the date with Hinagiku at that expensive restaurant in Mykonos?

The chapter where Hayate allegedly returned to the past is actually from the Volume 4 extra/Anime S1 Episode 51. You can read the chapter from this link:
http://www.tenmanga.com/chapter/Hayate-the-Combat-Butler-------------------Ch-004-5--Radical-Dreamers/199711/

Regarding the date with Hinagiku, its from Chapter 237 to 239.