Increase of distance per week

Last night I did 3000 yards: 600 warm up, 1750 yd (1 mi) in about 29 min., then more to get the 3000.
I figured up how much to increase each week, according to my Open Water Swimming book by Penny Dean which says one can increase by 5 to 15% each week. I can increase by 6% each week to get up to 6000 yards by May 13, the day of my last long swim. It isn't so much the yardage that scares me but finding the time to get such long workouts in. Some days I can only do an hour due to work/home/pool schedule; other days I will need to be in the water for 1 1/2 hours or more. Saturdays may be the time for that, making sure they give me a lane line since Sat. is only rec swim. I have to plan ahead so there is food at home ready to heat up too.