For those struggling with progression and unlocks, get the girls with higher awareness to 5 hearts, and finish the day with no timestop uses left. That will give you a cutscene which unlocks the next type of school and will then allow you to buy the next tier of upgrades.
Be warned, it is INCREDIBLY grindy. Even maximising PP (money) on every girl takes hours of doing the same thing over and over again just to buy another couple of upgrades to then do the same exact thing the next day to maximise profit to buy said upgrades. The final animations are nice, but not worth the hours of grinding to get there in my opinion.
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My "strategy" was to upgrade consciousness and time as much as possible, with lust speed afterwards. I only upgraded finger to level 4. Use level 1 interaction everywhere possible to get to 2 hearts ASAP. Stop all interactions and level up. Use level 2 interaction on 3 or 4 places depending on your consciousness upgrade level. Stop interactions when you can level up to 3. Level up to 3 hearts and use level 3 interaction on crotch (+1 other if consciousness allows). Level up to 4 hearts and just keep level 4 interaction on crotch (have a YouTube video on or something at the same time at this point as you're just waiting for the bar to slowly fill). Then if you have enough time and lust speed upgrade, you'll be able to quickly level up to 5 hearts just before you run out of time but likely won't be able to do a single interaction without consciousness increasing. The amount of PP earned will turn green if it's the maximum you can gain from that particular awareness level girl.
Level 4 and 5 interactions are obviously what we all want in this game, but earning enough PP to unlock them and the upgrades to be able to use them on girls that'll still give you lots more PP to still upgrade more is in my opinion far too grindy, to the point where the game was a background focus for me whilst I did or watched something else at the same time. Again, great concept for a game, but give us the later rewards without it being such a grind. I came to play, not wait and watch to then be dissatisfied with how little extra I could do day to day.