Predictive scaling scales the number of instances at the beginning of each hour.
At the head of next hour, predictive scaling is forecasting capacity of 5 instances
Predictive scaling starts launching instances 5 minutes before the head of the hour, because you have set SchedulingBufferTime as 300 seconds (5 minutes).
Predictive scaling starts launching instances only beginning of each hour, therefore you have to wait for the current hour to end before you can see the actual launch of 5 instances. To save time and continue with the workshop you can back to this step by end of hour and compare ASG activity.
aws autoscaling describe-policies \ --auto-scaling-group-name 'ec2-workshop-asg'