555 fading in&out if possible with pwm & led array
Try connecting a slow monostable 555 oscillator to a simple, shift register frequency divider. This way you can shift the pulses in and they will stay on until the shift register is cleared.

Learn more about shift registers here:
http://www.allaboutcircuits.com/vol_4/chpt_12/1.html

Shift Registers as frequency dividers: (Not nearly as hard as it looks BTW)
http://www.allaboutcircuits.com/vol_4/chpt_12/6.html

Using shift registers would eliminate the need for multiple 555 timers in your circuit and could greatly simplify the design because there is a constant time interval between lights lighting up.

I hope this solves your challenge!