ttlinMillis follows the other TTL caches i'm afraid though. So i guess its being referentially consistent closer to where it is? Not sure which ones should go to the other overall..

Also the function name is to align with the non-mutable cache variety

I'm not really opposed to a default capacity, but with any cache TTL or otherwise there's no getting away from how much memory your going to/willing to use? I'd personally rather the user thinks about it, if we were to let them think purely in time it should default to a very large value which then could lead to OOM's or other fun ? A TTL with a default size of 16 would make it by default probably not all that useful? (it would also appear arbitrary here to take the linked hash map's default)