How long depends on the County. It takes 6-8 months in Charlotte right now. Until the charge is expunged it will appear on your record as dismissed. You best disclose and explain in any applications or wait for it to clear from your record if possible and many places assume guilt even if the case was dismissed. You really need to follow-up with your County if you need to do anything else. In Mecklenburg you just fill out and turn in. In Union County they put it on for a hearing you must attend.
As a former Assistant District Attorney I will echo what has already been said. The amount of time and the level of court formalities will vary. It is best that you seek the help of a Raleigh attorney to help you with the situation.
Now as to the issue of who will see the expungement, it will never "completely" go away. The State of NC will always keep records of what has been expunged in Raleigh. If an FBI background check is performed on you they will still be able to see what was expunged. However, your standard employer background check will NOT show your previous charge.
NC does report all of there crimes, as does every other state, to a National Data Base. Prosecutors and law enforcement officers frequently use these "National" Checks when determining record levels for sentencing. However, if your case is expunged it will likely not show.
As to whether you should mention your previous CONVICTIONS on a employment application that depends largely on what it is asking. If it is asking about whether you were ever CHARGED honesty is the best policy. However, I believe expunging your record will go a long way and make a potential employer more at ease with hiring you.
Nothing in this question should be taken as legal advice or resulting in an attorney/client relationship. Anyone facing a legal issue of this kind should speak to an attorney personally about their legal options, giving them the full facts of their particular situation.
We typically tell clients that it will take 4-12 months due to the State budget cuts. The paperwork is sent by you or your attorney to Raleigh, SBI, back to your county for Judge's signature, back to Raleigh. The fewer charges you are trying to expunge the less time it typically takes.
As for how you will be notified: Raleigh sends the paperwork back to the Clerks office to get another signature from the Judge. In my area, the clerks will notify us once it comes in. Once that signature is obtained by you or your attorney, the Clerks office sends back to Raleigh.
When speaking to a potential employer, be sure to PAY ATTENTION TO THE QUESTION PRESENTED! If asked if you have ever been convicted...no. Charged...technically yes. However, I would argue that the fact that the charges were expunged you have a right to answer no. If they ask about being charged and it includes expunction then you must answer yes. Like I said, it really depends on the question.
The criminal background should not show the charge at all once the expunction process has been completed by the local clerks office, SBI and Raleigh.
Any advice given does not enter the Attorney and person asking the question into any privileged relationship.