Login screen timeout

This has been asked before, but there has been no satisfactory answer.

I'd like the login screen (where I type my password) to stay up longer before it fades back to sleep. Right now that time is so short as to be cruel, something like 20 seconds maybe. Now PLEASE pause and read this again, before you start to bang an answer. This is NOT about the time after which the computer sleeps when inactive. It has nothing to do with that. It is ONLY about the login screen.

I usually login in the morning, when my fingers are frozen and there are dozens of stupid house chores to take me from the computer. It is supremely irritating to open the screen, get the login dialog, be distracted, come back and see that computer is sleeping again.