Define default length for Feature Merged

We slice and dice our gantt chart by 3 week chunks (to align with our sprints in Jira). It'd save a lot of time resizing features if we could override the default 5 day length by defining a custom feature length at a product level (or even at a release template level - as we can already define release phase lengths there). We'd set this our override as 21 days instead of the default 5 days, and we'd then only have to align the start/end dates as necessary without having to resize every. single. feature.