Chris Carmichael once said that an indoor ride is 20% harder than outdoors for the very reason you describe. Not 20% more intense, but as you’ve pointed out, 20% more pedaling.
But, no, I would not adjust accordingly. Time in the saddle is critical. Your brain and muscles need to get used to long durations, and the workout duration in your plan are appropriate and important for improving fitness.
I prefer to think of it he opposite way: you should consider adding 20% MORE time to outdoor riding because of how “easy” it is before you consider chopping 20% from your indoor rides.