yeah, its pretty clear to me that these achievements were designed with a timescale in mind. there's the super easy "play tidal trouble" style achievements that can be achieved within a few minutes/hours, but then once those easy ones are done there needs to be more challenging stuff. the 123 xyz and "breed x ancients" one speaks to this - i like that there's achievements that will require months if not years of planning and gameplay to get. keeps the system feeling fresh and makes you approach the game in a new way.

although i was thinking that if someone really whaled and bought thousands of boons of fertility, they could get those breeding based achievements in a day or so by buying tons of non-BCD fodder adults, booning them, then mass exalting all the hatchlings and repeating until they get the achievement. but it would probably cost around a million gems in boons to get both the modern and ancient breeding achievements