The way I read it is theoretically you could do the 30-hour thing a maximum of 6 times of year. According to the letter, the 30-hour rule applies...
During March AND April every year
When your congregation receives its regular CO visit
So if by chance both of your CO visits don't fall on March or April AND each visit happens to be spread out over two calendar months, then you could do 30 hours 6 times! Conversely, the minimum times it could happen would be 3. So, every year a publisher could aux. pioneer for 30 hours between 3 and 6 times depending on their congregation's CO schedule.
Seems like a headache to keep track of!
Imagine this scenario:
Service Overseer: Brother, I see you only got 30 hours when you auxillary pioneered in February. What happened?
Publisher: Don't you remember? This year was a leap year so there was an extra day in February. The last day of February was the first day of the CO visit. I thought we could put in only 30 hours if the CO was visiting.
Service Overseer: Oh right. (Shakes head and starts talking to himself.)