Estimates will vary greatly based on the size and experience of the team.
Part of the job of a project lead is to break down the work into manageable chunks. This is largely where we design the system to be built. Hint: this part is missing in a lot of dev processes.
Below two weeks or so of work, the ownership should be given directly to the engineer who will do the work. If they say yes, then we're good. As I told someone earlier, I hate "story points" with a fiery passion.
Binder