"Well ofcourse you should strike while a lead is hot...isn't that way too obvious a statement to make?", you might be thinking. However in practice, it isn't always followed by companies even those equipped with state-of-the-art . Leads which display a sudden spike in activity levels and can be scored higher are ones that are calling out to be contacted and followed up with personally by sales. If leads that have been nurtured to the point they have reached a level where they are "ready" and then allowed to sit idle for a longer period without being engaged by sales, the effect of the nurturing process will wear off after some time and that lead will "cool" down and eventually go to the bottom of the nurturing cycle where it probably started.
Going by the second objective which is , a "sales ready" state would be reached when a lead has responded actively to your content consistently enough to know that some level of interest has been achieved. A level enough for sales to take over from. The constant messages, content and reach outs are all focused on driving a lead to this state and when a lead has reached this level, it's time to act.
So if you have a nurturing program in place and have the technology to track lead activity and identify ready leads, make the most of it and strike while the lead is hot.