@mathewbeall, good question. No, the Iro does not adjust the watering duration, only the frequency of waterings. For details on Flex Schedules, please refer to this support article.
Fixed schedules will skip schedules based on your Weather Intelligence settings. You can enable the Water Budgeting feature for automated weekly seasonal adjustments.
Just curious, did you configure all of your zones with the correct vegetation, soil type, nozzle (precip rate), etc?
Hope this helps