Vacation on the 15 and 18 day schedules is pretty much the same. You get your week that you bid for and they give you a lead in of 4 days off before and then 4 days off after the bid week to bring it to 15 days. On the 18 day you can bid for a block of up to 3 days off before it and you will find out by the 15th of the month before your vacation if you got those days. You can also bid a block after it since we can bid for 2 separate 3 day blocks of time off per month. I would guess it's unlikely to get both 3 day blocks you asked for within the same month, but it is possible. I bid my vacations so that they would flow from one month into the next to make it more likely to get 3 days before and 3 days after (stretching it to 21 days). I got the first 3 and I'll find out by the 15th of next month if I got the last three to make a full 21 off in a row. In theory you could end up with more time than that off since it's a fixed schedule that you bid on on-line, but they make each schedule by hand and I guess if they like you it is possible for good things. The 15 day schedule will get you a minimum of 15 days off in a row for vacation and they will tell you what they project for you to work, but no extra days around the vacation are for sure off unless you finished a trip 1 to 3 days before the beginning of your vacation. I hope this helps and doesn't just make everything more confused.