Aneon made a good tutorial on how to do the skips consistently. Can be found here

Some more testing, with a 60hz turbo these skips become free to do. Can get perfect menu buffering every time, so I did a run of Memoria and skipped all the bosses first try(except Deathguise because I forgot)

So the setup I used for this is a program called Joytokey to get my xbox 360 controller to have turbo on. I have menu and cancel set to repeat 30 times a second and I timed pressing them to have them alternate to buffer perfectly. Thinking about it setting them to 15 times a second each might make it more consistent.

It's a good 4 minutes or more time save thanks to these skips. So maybe 15 minutes or so in a normal run if consistent methods are found for non-booster buffering, my turbo settings weren't consistent when trying Prison Cage without boosters, and using scripts aren't allowed for it in runs I believe.

Yeah Iifa tree plays out as normal if you go straight there, but there must be something that needs to be triggered in Madain Sari during the first visit for Soulcage to activate.

For Hedgehog Pie, when you get control of Cid you go left and buffer through the loading zone instead. Got it first try, but failing it isn't a big deal since it just moves you back a bit. Didn't try it un-boostered, but should be possible if the trigger doesn't extend too far, so that would be a huge save for normal any% run too.

I've tested up until Oeilvert. Prison cage is definitely the biggest save so far. Skipping the moogle cutscene is a small time save, but you need to do the extra battle to get the key, and I couldn't get the skip consistently so I don't feel its worth it yet. Madain Sari is almost skippable, can buffer through the Iifa tree barrier and get down to the bottom, but the trigger for Soulcage doesn't load and the game softlocks. The Hedgehog Pie minigame can be skipped easily. I couldn't get a skip of the Black Mage fight in Burmecia to work, but might be possible still. Other than that I haven't found anything else workable.

Got an extra bell by fighting the black mage during Gizamalukes grotto and then skipped the moogle cutscene, whether that saves time or not I dunno, but it's something. This menu buffer skip could be used so many places, so many possibilities. Just need to find a way of making it consistent.

Lich skipped as well now, with boosters active. Skipped Deathguise in this video too, though that one was known about before, and learning that got me hunting for more.

Adding on to this, I've now managed to skip the Maliris fight, as well as the Alexandria cutscene that follows after it. Done with the 4x speed booster on. Need to test if they can be skipped normally now. I've also managed to skip Tiamat, but i don't have a video of that one yet.

I managed to menu buffer over the Prison Cage fight trigger without the speed booster turned on. This skips both Prison Cage fights, all the walking around the crashed ship and the Baku fight.

Based on the first place run this saves up to 9 minutes straight away. The second thing this does is skip the trance activation. From my testing so far it stays deactivated, so no more losing time to trance animations. Vivi still trances in the Black Waltz 3 fight, but the trance bars don't appear afterwards.

To do the skip I have my Y button set to repeat 30 times a second, so I hold Y and up, then cancel out of the menu each time it pops up. Haven't managed to get it consistently though.