What do I care about start to finish time?
The only way to shorten that latency would be to have so many employees that they can all spend all day just waiting to pounce immediately on their inbox. It's just the same or worse waste distributed differently.
A developer with a full pipeline seems the most efficient to me. Let there be 15 projects all in different stages of progress.
It's fundamentally not a synchronous process and I say a mistake to try to make it one.
Edit to address a sense I'm getting from several comments at once, that I may be a manager who doesn't understand or care about developers:
I AM the developer (& sysadmin) with a bunch of fresh and stale projects and it doesn't bother me at all. I always have work to do but it's not stressfull because that is about your boss(es) not about the number of open items. If anyone tried to say all that stuff needs to be done yesterday, sure that would be a problem. But all they really are is a spectrum of priorities. Some are just ideas little more than stubs for possible future interest, some would be nice but may never be justifiable in a strict easily quanifiable sense, you can't bill any customer for the hours, and yet would still be nice, would be one of the things that sets your product apart and attracts the customer in the first place, and some have normal priority, and when something high priority comes along, it simply displaces the rest. It just requires a boss who doesn't say that every single new item is always the most important.
That stack of available projects, and the age of half of them, doesn't bother me at all. Half the time, a different project is as good as a walk in the park for the reset / fresh look factor when stuck on something.