I've run sub 2:40 five times. After the first time I did it I boiled down the schedule to the below week. If I do it for 8-10 weeks I will be in sub 2:40 shape. I would advise taking a month to just build up to doing the entire week, so 12 weeks total.
Monday - 60 minutes easy
Tuesday - 90 to 110 minutes easy
Wednesday - 60 minutes total. 3 weeks of 20 x (200M by 200M fartlek). First 200M should be current 10K effort and second 200M marathon effort. Change this to 400's, then 600's, 800's, 1K's, mile repeats. 5 miles total. Repeats always at 10K effort. 90 to 100 seconds rest.
Thursday - 90 to 110 minutes easy
Friday - 40 minutes easy
Saturday - 75 minutes total. 50 to 60 minute tempo @ 82-85% max HR. You can work this up as high as 90%.
Sunday - Long, 120 minutes building up to 150 minutes.
I've tried tweaking this but have found that the key elements are the 3 long runs and the Saturday workout.
If you can't run 10 miles under 60 minutes any day of the week you won't break 2:40. Before I had broken 2:40 I had run many halves under 1:20. If you are not running long frequently it won't matter.
You can do it with consistent work at marathon effort and volume. DO NOT think miles, put in the time.