calculate how much time you have to ride, how much you plan on getting in during the week (i'd say at least 15mi a day - with a rest day before you push it on the weekends) then take the next couple of days light rides at a slow pace before you push again to recover. Then try pushing an extra 3-5 miles every weekend. Remember that the real long ms 150 trip is not a race and you can take however long you need to recover afterwards as well. Don't push yourself too hard and overreach/train though.