The rest days in Couch to 5K are not there to give a break for lazy oafs who don't have the willpower to run every day!! They are there as an essential part of the programme.
To expand on something kaffeeg said, a key objective is to make your body adapt to the needs of running. In order to do that, it needs to build new blood vessels, add mass to muscle fibres, strengthen tendons, literally slightly change the shape of your bones etc etc. It cannot do that if you are constantly making it run run run and you are very likely to damage something if you carry on. The rest days are there to allow your body to make these adaptions.
If you want to keep exercising, then do some strengthening exercises, or do some other non-impact cross training - swimming for example.
Ah... I'd forgotten about that! "less than 4.80s" was indeed where both the above posts were cut off, thanks.
I did go on to comment that I guessed that tom's time for a 35m must be about 5.00s dead, but he could perhaps do a test of that distance. That would class as "good" for a man, but I'd say that it would be very good or excellent for a beginner aged 16.
The procedure dictated by brainmac is to do 3 runs, and to count the best of the three, so tom's right to give 5.45s for his 40m time.
brianmac also gives a reference to a book with further reading on this 35m test, and what constitutes a good time.