Wanted to add my voice to the list as ... me too.
I've been postponing that darn "software updates available" for days and weeks, since I got Mavericks (up from Mountain Lion), till I find it suitable to not have my system cut away for an update randomly. .
Whoever thought 10min, 2hrs, tomorrow - were appropriate. How hard would it be to add the option of n hours or n days???
How hard would it be to let it download in the background AND then give another prompt to apply update now or in x hours or with next startup?
Out of frustration I let it update today. Only to find my internet bogged down, worked on a spreadsheet, answered the phone, looked away from the screen, poof, black screen? Update being applied for the next 20 min. Forget about that spreadsheet you were editing, billing you have to do and a couple mails you have to reply. Just wait it out.
It is not the end of the world, but it is completely non-productive and utter crap that after the download it cuts away, no warning, no delay, ... you're out for however long it takes.
That's the kind of thing which makes people turn updates off altogether.
Anyway. I sent Apple another note about this horrible software alert notification system and update implementation. Hopefully it was already on the Yosemite fix list as one of the new 200 "features". If not, I hate to think about more years of frustration and productivity loss everybody endures on work systems.
PS: Come to think of it. I probably had updates or notifications disabled under mountain lion. ... oh the joys of a newer computer and newer OS 😉