if it's marketing the feature list and time schedule are paramount, everything else must adapt.
if it's not marketing the business can still make the choice between
1. deploying the feature on time but at poor quality.
2. deploying the feature late, but with good quality
3. deploying on time with good quality, but dropping the feature until next time.
one very good thing about time based releases is that you have a pretty good idea what "next time" is, and if it's a relativly short cycle it's not that big a deal to drop the feature for one cycle. If your cycles are unpredictable, it becomes a very big deal to drop a feature (because you don't know how many years it may be before that feature becomes available)
In general I'm a big fan of having fairly frequent time-based releases, but you do need to be aware of the trap that marketing people will try to push you into and avoid it.