If you bring people in at the beginning you get two benefits: they know what’s happening (so they know what’s coming and can work it into their planning down the track), and they can add their creativity and general brilliance immediately where it might have instant impact (and they can still noodle on things as they prepare for when it’s their time to play).

If you bring them in only when their deliverable is needed, you save a little time and leave them a little head space to focus only on the actual deliverables.

One option implies and relies on their value in all its glory.

The other rests on the idea that the benefit comes from a single point of focus.

One treats them as a partner.

The other as a resource.

You decide which you want.

Skippy strategy: To benefit from their general brilliance, treat them as a partner.