In 2012, no state introduced more failures than Florida. The average wait time to vote in the state topped 45 minutes, according to data from MIT's Charles Stewart. That's 31 minutes longer than the national average.
(Oregon and Washington, which largely or excluively use mail-in ballots, aren't included above.)
That doesn't mean that Florida voters need to build in 45 minutes when calculating how much time to dedicate to voting on Tuesday, however. First of all, the 2012 waits were down from 2008, suggesting that states are getting better about working out the kinks. Plus, midterm elections have far lower rates of turnout.
Wait times are also not uniform within states. More populous areas were more likely to see longer waits, with counties that had populations over 150,000 seeing above-average waits and smaller counties seeing below-average ones. This correlates to racial breakdowns, as you might expect; black and Hispanic voters had to wait over 20 minutes on average, while white voters waited about 13. The differences largely related to the availability of voting locations and machines. In Florida, early voting is up over 2010 -- and the fewer people who need to vote on Election Day should mean an easier time at the polls for everyone else.
The data from Stewart includes interviews with thousands of voters in hundreds of counties across the country, in which they described, among many other things, how long they had to wait. We took that data and, for counties with responses, calculated the average wait time in 2012.
Not every county is included and the data here is only anecdotal, but you can see the wide disparity in wait times by area. (Click each county to see how many responses were provided, which should be considered before you start stressing out about things too much.)
So what time should you get to the polling place to have voted by a particular time tomorrow? Well, assuming wait times are the same as 2012 (an unfair assumption) and that wait times are uniform throughout the day and throughout the state (also unfair), you should plan on it taking about 15 minutes. And remember that polls open and close at different times, so you'll want to double-check that, as well.
One other thing, that we cannot stress enough: Remember that the volunteers at polling place are not the reason things are going slowly or quickly. They, too, are simply tiny parts of the huge, lumbering, creaking process that determines which people get to boss us around for two to six years. Democracy: It's the best!™