Using the split-stub dumps, or the toolserver are both good ideas.
But suppose you wanted to use the API; the question would be: do you
want the exact timestamp for the creation of the page, or are you
looking for the date? Given the answer to be that you want the
date(s), you might proceed like this:
For every 1000th pageid, get the earliest rev and note the date and
time. (If a given ID is missing, i.e. deleted, hunt around it, +1, -1,
+2, -2 etc 'till you find one.)
To get the date and time for a particular pageid, interpolate between
the next higher and lower 1000th. This should pretty much always get
you the correct date, with some chance of it being off by one for
pages created near midnight UTC.
A bit of testing will show you if this is accurate enough for your
purpose; read the 1000ths for a small range, then pick some random
pageids within that range and compare the interpolation with the
actual first revision time.
best, Robert