Richard, thanks for your help - that works a treat. I've changed the value in the first line for testing, but using the following code it changes from night to dawn, ramps up to 100%, changes to day, then to dusk at the set time, and fades down to 0% and changes to night - in 12 minutes. I'll reset the value to 7 and see how long the cycle lasts.

Code:
case DAWN 
lcdout $FE,$80+13,"DAWN "   
if ss//1= 0 then
if ss != old_ss then
B_PWM=B_PWM+1
old_ss=ss
endif
endif
if B_PWM = b_max then
Blue_Day_Cycle = DAY
endif

case DAY
lcdout $FE,$80+13,"DAY  "
if counter1 =1208 then
Blue_day_cycle = DUSK
endif
    
CASE DUSK
lcdout $FE,$80+13,"DUSK "
if ss//1= 0 then
if ss != old_ss then
B_PWM=B_PWM-1
old_ss=ss
endif
endif
if B_PWM = b_min then 
Blue_Day_Cycle = NIGHT
endif

case NIGHT
lcdout $FE,$80+13,"NIGHT"
if HH = S2H and MM = S2M then
Blue_Day_Cycle = DAWN
endif
Now as I want to learn from this experience, can you please explain the use of the double forward slash and exclamation mark