The 'time limit' on daemonic presence in the matterium seems primarily linked to the idea of their "power" when they are fully physically manifesting. that is, they're doing it through their own powers, rather than through the possession of a material link (read: daemonhost) to the, well, matterium.
King in Farseer implies that the length of possession can be related to the strength of a psyker, though Abnett and his 'daemonhosts' would tend to imply that any individual can have a daemon possessing them. Of course, that's an obvious difference: a pysker can be possessed by a daemon, while a daemonhost is summoned and bound.
As to how much control a daemon has while in the material realm? Well, they maintain their daemonic powers and can use this to shape the material realm, as well as their own body. (Of course, the implications from Pawn of Chaos is that the outer body will eventually take on the form of the possessing daemon, but make of that what you will.) And, yes, the lifespan of "suitable" hosts can have their lifespans expended.
IIRC. It's been a while since I looked at this type of thing.
In short, you might want to pick up Farseer and Eisenhorn just to get a feel, if you haven't done so already.
Kage