Granted everything differs as far as shedules of shows depending on what day you go. For example, if you went during a non peak time, especially in february, there are usually only 2 or 3 showings of the live shows in the park. So if you miss both, then yes, you dont get to see that attraction that day. On a peak day shows have upwards of 10+ shows a day. Usually they are every hour plus 10 min apart. As an employee there I guess I have to be biased because I know the routes of ways to go and schedules of everything but still, the point I am trying to make is, Universal has 12 attractions in the park. Disneyland has 12 attractions in Fantasyland alone! So what I am trying to say is, given that only a few of the attractions at USH are over 20min long. It is very much possible to do everything withing one day. Peak or non peak. The trick is, like at any theme park, is do the biggest and best attractions as early as possible to avoid long lines later on that day. The studio tour takes 45 min and rarely goes over that. If you get on that with no wait, you're back within an hour, as opposed to having to wait 30min then another 45min on the ride itself, it eats up a lot of time.
It all depends on how much time you take strolling through the park. Like mentioned above, USH doesn't have the atmosphere that Disneyland does, so a lot of the time, you won't find yourself just oooing and aahhhing at the surroundings.