For solo this shouldnt be an issue seeing drops remain on the screen until you click engage or return to town, so in theory you have as much time as you want.
The only exclusion to this is if you're solo whistling, where obviously you wont wait after each wave of mobs, you keep spamming the engage hotkey or when exploring and fighting normal mobs, in general these drops are mostly crud anyway, if you're using high ML then you might be looking a bit more closely, even then, the only occasion of missing something i would have liked to have picked up is when running around with full inventory.
My personal opinion is we have enough time but for the purposes of this debate i wouldnt be worried if people wanted increased timers, so voting banana as i'm not worried if this is a setting in options, i would leave it as is.