We’ve been to Universal twice and only planned for two days. Next trip, we’re planning to stay four nights, so we’ll have three full days at the parks, plus some time the day we arrive and check out to explore a bit. We’ve made over a dozen trips to WDW and were very pleasantly surprised at how much we enjoyed Universal. Our last trip, our youngest was too short to ride a good number of rides, but she should be good for the majority of attractions. We absolutely plan to stay on site (probably RPR), so we can use the express pass. I can’t see making a week of just those parks. But if you stay onsite and take day trips, absolutely.