When to get Ballistics & Thumb ring?

When I'm going for an archer strat, I tend to go 2x ranges in Feudal with Fletching then add a 3rd range after clicking up if I can afford the wood. When I hit Castle, I get Crossbow, Bodkin and Bow Saw. But I was wondering when is the best time to get Ballistics & Thumb ring? Like how many units do you need before it's cost-effective to get these upgrades? I usually delay these a while so I can use the resources to buy more units and put down TCs but sometimes feel like I'm clicking them too late. Is there a general consensus on timing or is it just when you can afford it / when you have enough units?