The biggest issue with Universal is the show times, and forces folks to take one full day and miss some things, usually shows. And while the FOTL pass helps, you still had the show times problem.
So IMHO, it is 1.5 day park, maybe 2 full days depending on how much shopping and hanging around the Wizardly World and if you bought a wand, etc.
And that is just inside the park, add Universal Citywalk, and you can make it a third day.
So I would plan 2 full days, and if you can afford it, get a FOTL and focus on the rides and using it. Then on day 2, work on the shows, and do the shopping and minor stuff in between, since those can be flexible in time, unlike a wait in a regular queue where you commit to it, and not 100% sure when you will exit. For example, the tram tour is planned to be just under an hour, but due to actual filming that day, it can be shorter or longer, and there are other issues that can make a tram tour longer. I think my longest was over a hour and half from driving away from loading, to getting to the unloading area. (I am not counting the extra time it takes to open the fences/gate doors and then walking to the exit. That can be delayed for safety reasons)