There may not be an average sentence under those circumstances. Every case is different and turns on different facts. Six months seems high under the circumstances you describe, but there may be some important facts missing from your description. Your father should consult with a lawyer about asking the judge to reconsider, or seeking an appeal, if there is still time.
This response does not create an attorney client relationship and is offered for informational purposes only. Only a lawyer fully versed on the facts and circumstances of your case can properly advise you on the case. I am licensed to practice in Minnesota, not every state. You should always consult with an attorney licensed in your area on how best to proceed.
A show cause hearing usually means this is your 3rd, 4th, or 5th mistake, not your first mistake. It usually happens in civil cases when one party will not do their part in the discovery stage of the case. Discovery is an unfriendly game of cards: you show me yours and I will show you mine, and whomever has the worst hand has to settle by paying the person with the best hand or risk going to trial and probably paying a lot more.
I really don't know how any one attorney can come up with an average. If you find 3 or 5 attorneys that have been around a long time in different parts of Florida who can tell you the average, let me know. I'm sure they have seen everything from 1 day to 30 days, but 6 months? I'd say that is very rare.
I won't say criminal contempt is rare, but its not really all that common--6 months has to be very rare and something is really irritating the judge. Anyway, it may just depend on the judge's mood that day, but legally, the judge is supposed to decide just how bad this contempt was and come up with a sentence/punishment to match. BY THE TIME SOMEONE GETS TO A SHOW CAUSE HEARING, a lot of deadlines have been missed or a lot of continuances have been granted. The judge is ALREADY upset.
The show cause hearing basically means, "I think you have been messing around with this case and the taxpayers money (paying judges, clerks, etc.), I'm fed up, now you tell me why I should not hold you in contempt." Basically, the burden of proof is now reversed and the contemptor has to prove that he is innocent (or that it has not been his fault) this time and the other 2, 3, 4 or 5 times. It may just be a big pet-peeve of that particular judge. The courts are really short on money and if the judge's think anyone is wasting the court's money, they will be harsh.