cotyledons curling and becoming hard day 7

Not sure what the problem is and whether it is something to worry about, I'm on day 7 of a 300watt cfl closet grow using coco. If anyone could lend a hand in diagnosing the problem?

Can't see a problem

I wouldn't worry. The cotyledons are embrionic leaves. They are full of the nutrients your plant needs in it's first days of life. You will notice that they are firmer and almost "puffy" in appearance. This is because they serve two functions, they are a reserve for water and mobile nutrients and they are the initial solar panels for your plant. As a plant matures it no longer needs them. They will swell and shrink in size a little with watering and when the true leaves appear they will fade in colour then shrivel and drop.

Yours do not appear to be near that stage yet, they still have a healthy colour and shape IMO.

Keep doing what you are doing.