Actually, you can plant as soon as the last hard frost is past. As long as the sun is gaining each day, and the length is over 12 hrs, and the plant gets at least 5 hours of direct sunlight, it will veg.
Think of it this way.... in the wild, weed disperses its seeds upon death in the late fall. The following spring, it pops....it doesn't wait for 14 hours of daylight. It pops when enough moisture and warmth heats the ground, and that's it.
Here is a useful link. You can make a yearly, or monthly calendar according to day length here... www.sunrisesunset.com
True that, my boy is planning a guerrilla grow, and he is planting some well vegged out and hardened Super Lemon Haze clones the day of vernal equinox.