Runners: By now you should have worked out an achievable time to aim for on big day. Be conservative, it is far better to have a pleasant experience on race day than suffer because you over-estimated you fitness. After all, there is always next year!
Day One: 45 minute steady paced run.
Day Two: 25 minute easy paced run.
Day Three: 4 X 5 minutes with 3 minutes slow jog recovery.
Day Four: 30 minutes steady paced run.
Walkers: 4 x 35 minute walks on alternating days during the week and a 70 minute walk on the weekend.
You should be really feeling the benefits of your walking program now and should be able to handle the increase without much trouble.