When I was 18 I picked up Arnold Schwarzenneger Encyclopedia of Bodybuilding and started doing his competition workout program. This worked for about 2 weeks, and then I found myself mentally not wanting to workout (sign of over-training) and always being slightly injured in one way or another(another sign of over-training). I then bounced back and forth between not training at all and going all out 100% for awhile until I figured out what I personally needed to do.
What I mean is that what works great for some people, will be absolutely non-functional for other people. You need to find out what level your body can perform at, and then go from there. Everyone on this website could tell you how many times you can do pushups/situps/whatever, but the bottom line is that you are an individual with specific abilities and needs. There is no set-in-stone scientific explanation to simpy do X amount of exercises Y times per week for Z amount of weeks to attain the results you want.
If 7 days works for you, great. If 5 works for you, great. 3 could be effective too. I can't tell you, and neither can anyone else.