if I remember correctly your fadein loop runs at 1 sec intervals therefore , 5 minutes = 300 seconds
increment is :- 4095/300 = 13.65
so the loop must inc the pwm value by 13 or 14

case DAWN
lcdout $FE,$80+15,"DAWN "
if ss//blue_delay_in = 0 then
if ss != old_ss_blue then
B_PWM=B_PWM+13
old_ss_blue=ss
endif
endif
if B_PWM = B_Mid then
Blue_Day_Cycle = MORN
endif