How easy/simple/realistic is it to play through this game without missing content? Time progressing seems like it might force you to miss loads?
If you're vigilant about farming Affection/Lust, and if you CAREFULLY read and pay attention, getting through without missing scenes isn't that hard.
1) One character will confess to having a crush on another of the girls, and ask that you let her take her shot before you make your move. If you ignore that, you'll miss a lot of content.
2) When you get an invitation to take a girl on a weekend excursion, the game will suggest that you spend some time with her roomate first. If you don't do that, you miss content later in the game.
3) There is a lot of content gated behind who you're sleeping with. If you say no to any of the characters, it will block future access.
The rest of the missed opportunities are going to be due to not having enough Lust points for a girl when a Lust scene happens, since those are fixed points. So either use a save editor to set the values to a higher number to avoid the grind, or make a point of grinding out a lot of the stat to prevent that.