[psidnell]

I think the conceptual problem here is that a task is "Available" if it's start date is in the past OR if it has no start date at all. There isn't a way to select only those items that have a start date in the past (that I know of).

I tend to use Flagged to achieve this: at the start of the day you'd look at any newly available tasks to see which ones you INTEND to start and flag them. After which - obviously - they'll show up in the flagged perspective.

I actually have custom perspective that filters on Flagged and Available that does the trick, so I can flag things in advance but with a start date in the future, and they only appear once the start date goes by.