I thought about that, but maybe not to `SimplePool` because it wouldn't then be so "simple" :smile: 

Further, if it was made generic the pool would have to wrap to item in order to associate the creation timestamp with the item.

In this case, we already have a wrapper so we'd have to wrap the wrapper.

Currently, the only other use of `SimplePool` is TCP, and it doesn't have the requirement (e.g. changed credentials).

(I just pushed a minor change to rename `epoch` to `created`).