"The effort length and instantaneous power output changes, of course."

but that's what the phrase is meant to convey, right?

Don't run through consumable X (energy/money/etc) like there's no tomorrow - even though there's <some big important milestone> now, we've got dozens more of those that we need to meet, so you're better off getting this one done at 75% than committing 100% to it and failing on all the others.

Don't work 12 hour days to get milestone X out, because there are dozens more milestones so don't get burnt on trying to get this one out yesterday. It would probably be more like, don't use 200% to get this out and then quit or burn yourself to 0% or a few % in a year when we want you to extend and maintain this stuff.

Yeah you're right, I hear it more like "this is a week long hike, not a sprint" as if a marathon included rest. In any length of racing there's no tomorrow. But I'm doing tongue-in-cheek pedanticness here and will stop that right now !