I think the surrender time should be 30 minutes, so it gives time to come back from a bad situation instead of just quitting altogether.
I was playing a game earlier today when we were doing bad, but still capable of catching up and winning. I in a small skirmish as Zed with the enemy ADC I believe, and then both teams end up showing up for a team fight. As soon as we started to fight, I was about to go into the thick of it on their ADC when all of the sudden the surrender vote pops up, preventing me from being able to move in the direction I need to as well as prevented my from casting my Ultimate... It was quite infuriating, except for the fact that we won the team fight and I managed to survive.
I hate the whole mentality of "We're not doing so hot, but we can just surrender in 5/10/15 minutes so it's okay, I can just do nothing until then." Obviously there's more of a punishment for leaving games than there is for running around and farming the jungle for 15 minutes straight, so people just wait until the 20 minute mark to surrender instead of taking the LeaverBuster punishment.. I think that encourages more trolls to just do what they want to do and then end the game quickly as opposed to being forced to wait it out until the game is actually over.
The down side is this: If the surrender time gets moved up, then instead of forcing them to wait it out, I believe that some people are going to take it upon themselves to feed as much as possible for the sake of ending the game faster, which is also unacceptable.
My point is, there's not really a whole lot Riot can do about the surrender vote without making the situation worse. Granted, there is a few adjustments that can be made, but with the server problems in the new patch, and the new champions, and fixing bugs, there's not a lot of time for little things like the surrender vote.
TL;DR - 1. Not much that can be done about surrender vote time
2. They should move time up to 30 minutes
3. #2 Will just encourage intentional feeding
4. Punishments should be more harsh (Not part of the rest of the post, but I think they should be)