Solo mining? From 1 second to infinity I guess. 
I was thinking about average time. There was such a counter for bitcoin a while ago I seem to recall.
Source: http://allchains.info/calc.html
My laptop knocks off 13 kH a second, I have access to quite a few other computers, and I don't even bother pool mining LTC. I found out pretty easily it wasn't worth it to lag all my processes and waste electricity. Would I have mined under those circumstances back when Reaper didn't exist? Yes, and I did earn a fair amount. The difficulty is reaching new highs, though, and it seems to be GPU or bust.
If you have a dedicated rig with good GPU's, go for it, but otherwise, I think buying them is the best option.