If you're going in for just silicone oil removal and there are no complications during surgery, it should be a really quick procedure (a few minutes). However, it can NOT be done in office, instead it requires a trip to the OR (so count on the total time spent to be a few hours: pre-op waiting+op+post-op waiting).
It varies depending on a number of factors and if any other type of surgery is being done at the same time. So you need to ask your surgeon for specifics.
JCH MD