I guess a lot would depend on your recent mileage. If you've been doing a fair amount of training, this could go well for you. You've probably at least heard of, or maybe even experienced, feeling pretty good the day after a race. I'm in my mid-30s, and I tried this (sort of) last year. I did a 12k on Saturday, and then doubled on Sunday: 2-mile and a 5-miler an hour apart.
After the 12k (which I ran very well in), I just did a very easy 2.5m cooldown, and was sure to rehydrate and refuel immediately after the race to speed the recovery process. The next day, I did a easy 2+ miles to warm up for the 2-miler. Then I ran it and felt completely lifeless. I had no energy. I jogged easy for about 15 minutes between the races and feared the worst for the upcoming 5-miler. Then about 2 minutes into that race I realized I felt great. I ended up only about 30 seconds off a PR, despite no competition, a steady rain, and a challenging course.
I don't know what you can take from this, but I think refueling/rehydrating after the first race is key. Also, you probably don't need to rest up or be as easy with your warm-up as you think on Sunday. Maybe even add in a few minutes of hard stuff to wake up your legs.
Good luck.