This is quite possibly one of the biggest (if not the biggest) question that is asked by anyone who is involved in the Social Security Disability appeal process. It is is not easy to answer for the simple reason that it depends on the variables.

Namely if a claimant with no knowledge of the Social Security Disability appeal system attempts to appeal a denial alone it could take long than usual, up to two years in some cases.
On the reverse side, someone with extensive experience in such matters (ie. Social Security Disability Attorney) can win an appeal in as little as 30 days.

There is simply no way to predict how long a case will take precisely because, unlike other programs (Department of Social Services, for instance), the federal disability program does not have deadlines for applications or appeals. Because of this, it is always best to secure a Social Security Disability attorney so that no time is wasted while waiting for benefits.

Roughly half of all disability claimants go on to request an appeal hearing which can take at least six months, but in some parts of the US, the wait is as long as 18 months or two years.