I've done 330 km in 3 days, but I was used to riding a lot.
Since you are fit, and with good cardio, on your first day you will ride something like 50-70km.
The next morning, you will be in hell:
- Your butt will express its displeasure in ways you can't possibly imagine. You see, in order to comfortably ride long distance, you first need a saddle that fits your butt well (it took me many tries to find that) and your butt also needs to get used to it. This takes a while, and many rides, starting short. With a saddle that suits you, and a hardened ass, riding all day is no problem... But with the wrong gear, it can be a nightmare, man.
- The muscles in your legs will be in pain. If you do jogging for example, your muscles may be exercised, but not in the same way that riding a bike requires.
- Your neck will hurt from looking up.
- And, since you didn't take the time to fit the bike properly (saddle position and height, handlebars, etc) the rest of you will probably feel like hell too.
- If you rode gravel roads (or anything without asphalt really) without proper equipment (ie, fat tyres or front suspension) your wrists will give up too.
You'll need 3 days of rest to get on the bike again!
At which point you will realize all the equipment you never truly tested will begin to break (like cheap saddlebags, cheap gloves, etc). Also, if the bike breaks down, you'll have no experience to fix it...
Also, on your first day, you will stop a hundred times to adjust your saddle, tune your bike, adjust the damn helmet strap that doesn't fit, realize your shoes give you blisters, and all sorts of tiny pet peeves that don't happen anymore when you got a bike and equipment setup that Just Works.
So... start from the beginning LOL