This is what I did when I did HIIT. It was more for endurance than fat loss, but works for both. I've since switched programs to bring my 5k time down more, but this is my suggestion:
10 min easy warmup
stretch
15min 30sec jog, 30sec full sprint
5 min cooldown
stretch.
It doesn't seem like much, but if you do it right you'll be hating yourself by the 6th or 7th set, and it will be hell getting to the end. But, like they say, you get out what you put in. I did this two days a week, my other stuff isn't relevant to you as I'm assuming you don't care much for endurance
