How long does it take an egg to hatch?

How long till a hatchling becomes and adolescent?

How long till it becomes an adult?

Egg -> Hatchling = 3 days
Hatchling -> Adolescent = 6 days
Egg -> Adolescent = 9 days
Adolescent -> Adult = 18 days
Overall
Egg -> Adult = 27 days

(I believe this is correct, not 100% sure)

What IvyCat said isn't always true, though. Eggs can hatch at 2 days or maybe 4 days, depending on how often they are nurtured. The same goes for hatchling to adolescent.

No, an egg will never take 4 days to hatch. 3 days/72 hours is the maximum time (how close an egg is to hatching exactly can be seen in their timer bar in their Genetics info section.)
Egglings gain age with clicks, with 5 correct nurtures adding 1 hour on their hatch timer.
Hatchlings get 'bonus maturity', so to say, from views, presumably also 5 views adding an hour to them, I' not entirely sure (once they're adolescent/adult, views give them extra exp)

As an example of what this can do, one of our bred baby nytes reached adolescence when it was 5 days old rather than 8- the accumulation of clicks as an egg and views as an adolescent.

oh.