Need some help! what am i doing wrong? (pictures included)

Alright, about two weeks ago I started my first indoor grow. I have them under a 400w MH bulb, for 18 hours of light, and 6 dark. There would be some days where'd I'd forget to turn the lights on, or off, ten or fifteen minutes late.
Well, heres a picture of all them..
The two in the back I think look fine, Its really the three in front that I'm worried about, especially the one on the right and left.

First the one on the left..
Its look okay except the those two big leafs coming out the sides, and how there curling on the edges.

Then the one on the right..
It kinda the same thing going on big, long, droopy leafs curling at the edges, and on top of that two of the leaves look like this..



Here's my grow setup..
This is only temporary because at the moment I have no power in my room, and I didn't want to run the lights on an extension cable. So, right now there in my basement. I put a heat mat under them to keep the roots warm, cause its a little cool down there. I also have a fan running so the light doesn't get the plants too hot. Like I said, there two weeks old, there lighting situation is 18/6, and I've been watering them once a day.
Any help would be greatly appreciated.

check pH try and keep the soil at 6.5-7.0... and ease up on the nutrients...

About you forgetting turning on/off the lights for just 15min i don't think it's a problem...
How far it's the bulb from the top of the plants?
Are you already feeding them? How much PPM's are you giving to them? You should not exceed more than 400 PPM in the 1st couple weeks of seedlings or even less...
Anyway it's looks like Heat excess to me, also you can't water them once a day or you will be overwatering the plants. Water every 2-3 days when the soil it's dry in the top about 1-2 inches.
Also what's the Temp in your room?
I hope this help.
Good Luck

The leaf tips curling down is from over-watering. As already mentioned, once a day is too much. Every 2-3 days is better. If the pot is drying out after 1 day then they should be replanted. The leaf with the messed up looking tips looks as if it was probably sitting on the soil when it was smallers, and is just dying. Cut of the bad parts and it should be fine.