I have heard a story recently by someone, who needed 3 attempts to get his first app into the AppStore.
The first time it was rejected because it wasn’t according to the style-guide, the second time because flaws concerning the usability. The third time it then finally passed.
Is it really that hard, to pass the Review-process?
Has someone already experience and can tell?
I think you will find that there are quite a number of people on this forum who have had Apps published on the App store. One of them might spot your post and provide some feedback on their experiences.
If you scan through the Journal category posts you might find some and get in touch with them by @TheirUserName
It depends on what your app is! I’ve had some pass the first try, others take 2-3 attempts
You should review the App Store guidelines or just google common App Store guideline issues
I agree with @mikaelacaron, it really depends on what App you’re trying to submit. You are also dealing with a real person, so if you think you followed all the requirements, try also to resubmit your work (If you’re lucky and someone from another department, not the original reviewer is looking at your code they can possibly let you in). I think I already did that a couple of times and it works. 
2-3 attempts? I wish! 
I am on my 6th attempt.
The good thing is, that you get instructions on what you need to change. But personally, I find the legal requirements challenging as they were not covered in any course here at CWC and I am hearing about all of them for the first time during the review process.
So how hard is it? I’d say it depends. You definitely should not have to meet a certain deadline for it to go live unless you are an expert 