I did 3 days in JOG and 4 days in Bali. While Bali was nice, I really enjoyed JOG, apart from the temples, the Javanese culture and meeting of people. We ventured into the city, ran into very friendly locals that took us to amazing little restaurants (one that had over 20 types of Sambal), saw the shadow puppet Ramayana with a Gamelan orchestra and others. While Bali is lovely, JOG is a very different experience, and it really depends what you are into. We even did a trek to some cave rapelling and tubing down a local river which was great - since we had a little more time. As others have said, if you want to hit the main sites (Borobudur and Prambanan) then 1.5 days will be sufficient.

We did have sunrise tours when we went end of 2019. The cab ride was awesome with the driver stopping on the way at a local mosque for a 4:00am prayer and then bringing some tea for us. While we didn't see the sunrise (it was very foggy and misty) the whole experience was surreal given the thick atmosphere. The Prambanan temples were great too, but we went mid-day and it was scorching hot. Also having seen temples across the Indian subcontinent, it was something I was a little more familiar with.