Don't use tinfoil. Doesn't reflect much light despite popular belief. Use mylar or cardboard painted ultra flat white (not glossy).

24 hrs of light is fine for seedlings until about 2-3 weeks old. By then they should be ready to transplant into a larger pot, if you started them in something small like jiffy cubes. After that switch to 18 hrs/day.

The first set of "marijuana-looking" leaves usually are the first to grow after it sprouts - it sprouts with 2 round leaves, then the next to grow are 2 marijuana shaped leaves, it sort of alternates back and forth until the seedling is more fully grown, sometimes more leaves per set, sometimes less. Varies with different types. They are very small to begin with though.

With absolute best condiditions it will take 1-2 months vegetative stage and another month or so to flower - about the earliest you can switch to flowering (change to 12 hrs light/day instead of 18) is when its about 12" high, like Proof stated.

If you're growing it behind your dresser it's unlikely that it will be ideal conditions there, so it will probably take much longer. What's your lighting setup?