Why doesn't it take place in release one you ask? The answer; impact.
Episode One is so heavily loaded with puzzles and choices, that to incorporate the inclusion of a ship bigger on the inside than the outside in a feasible narrative would be pushing it a little too far.That's not to say Episode One isn't without its dosage of Who'ishness though. You've got your Weeping Angels, your Autons and the Nestene Conciousness, Silurians and Cybermen, and perhaps even a Dalek or two?Top that off with a series of intricate and challenging puzzles, difficult choices that will heavily impact your later adventures in episodes to come and some pretty unique and interesting items (tease to Sonic Probe anyone?) and you'll hardly have time to think about the TARDIS.
Episode Two, which I can tease is a simple, to the point one-word title, takes place entirely within the ship. It leads on directly from the end of Episode One, and will give you a TARDIS experience unlike ever before.
So that should answer your questions, but for those that like to skim my increasingly long and detailed blogs:
Is the TARDIS to feature in Episode One?
Not directly, no
It's a development decision
How long between Episode One and Episode Two?
Other priorities mitigating, 2 months approx
There we go, stamped, sealed, delivered.