Here is the full list of all 9 Memory Lost-Pairs achievements.
UNDER 600 secs (TRIPLETS)
UNDER 400 secs (TRIPLETS)
UNDER 800 secs TRIPLETS
UNDER 350 secs (MEDIUM)
UNDER 290 secs (MEDIUM)
UNDER 230 secs (MEDIUM)
UNDER 60 secs (EASY)
UNDER 120 secs (EASY)
UNDER 80 seconds (EASY)