You asked what the 3 parts to a cycle were and how long it was.
1 .A cycle last for 3 weeks.
2. In the cycle there is 3 parts; a 5’s week and 3’s week and a 1’s week. In the original program the The 531 numbers referred to the the reps you are doing of the main movement during the workouts in that week. The 5’s week was 3 sets of 5 at increasing %. The 3 weeks was 3 sets of 3 at increasing % and the 1 week was a set of 5, followed by a set of 3, followed by a set of 1 at increasing %.
It gets a little confusing because later The program changed a little and instead of doing a 5 week a 3 week and a 1 week. The reps changed, for example in 5’s Pro every week was 3 sets of 5 reps. However what didn’t change is the % applied to the sets each week.
The program was originally designed to be once 3 week cycle followed by a delaod and then you increase the Training max by 5-10lbs and go again. This also changed later to be 2 cycles (6 weeks) followed by a deload hence the 7th week referred to above.