Generally speaking they require an operation, but not always. It is a very simple operation and should last no longer than 15-20 mins. I work in the Op Theatre though I have to say I've never seen one performed on a child so young. Have you been referred to a urological or general surgeon? He may not require an operation and they may decide to treat it without surgery.
Glad to hear you've got an appointment, it shouldn't be too long I guess, they don't hang about with children to be fair. They will sort his problem swiftly.
Most hydrocoeles self seal by 1 year, so I doubt the surgeon will want to do much yet, unless the hydrocoele is very large. They are due to the tube down which the testis travels (while the baby is developing in the womb) not closing fully.