Is it a good idea to go to apple for something other than buying an iPhone 5S today?

I bought an iPhone less than 14 days ago so I want to return it and get a 5S but I figure so many people will be in line and I don't know how long returns take. I don't want to be there for a long time returning it. I think it'd be rude for everyone else waiting in line. But then again I don't want to wait and then if the iPhones run out I won't be able to return this one or I'll have to go without a phone until I they restock on 5S iPhones.

Should I just go anyways? Does apple take too long when you make a return or will I be able to quickly return this phone and hopefully get the 5S without too much hustle? How long does apple usually take to restock on phones? Like if they run out today will they have more phones tomorrow? Next week?

It's my first time with an iPhone so I've never been to a store on opening day.

It all depends on how busy the local Apple store is, some are swamped on release days, while others are sparsely filled/lined out. There's insufficient data here to make a well educated guess here.