When subscribing you'll get access to the data immediately. When unsubscribing you'll continue to have access until the end of the calendar month.
This makes sense, since they charge you for the subscription for the month ahead. Like paying rent. You always pay forwards, not backwards.
Just remember that it takes 1 business day for unsubscribing, so don't do it in the very last day of the month or you might end up pay for the following as well.
No you pay for current month. If it is Nov 1st or later (like it is now) you pay for Nov. At least that is how TradeStation does it. Been so long since I used IB maybe they (and others) are different? Though doubt it.
Since I have never cancelled my subscription, I will never know if they pro-rate a refund by the day count. It basically works out to what I thought. You are paying for the month ahead, not the month behind.