Does this 4% distribution on the monthly balance have any dates or deadlines for this bonus to expire? ie if I have at least 1 BTX in my wallet will I always earn this monthly percentage?
As long as you have at least 1 BTX in your wallet you will receive every monday the "bonus" in percent set for the month (5% Jan, 6% Feb, 7% March, etc). You will continue to receive this as long as the aidrop wallet isn't empty.
There's a prediction by the user ypsi how long the airdrops will last with the current rates. I'm sure there will be an updated version of it as every monday. So, wait for it and see

Happy hodling and trading.