There is no time limit. Some events only progress after several days. Keep in mind that they might not trigger if you use cheats to skip time.
A small number of scenes are not repeatable. See p. 17 of the walkthrough.
Losing to enemies leads to a different scene than when you win obviously. If you want to see it, submit. If you want to see the victory scene, fight and win (requires lust, but too much lust can lead to defeat). Otherwise, it's best to avoid enemies IMO, unless you need to defeat them to progress a quest, or if you're after certain items (e.g. faerie dust), or you want to level up your combat spells (Fireball, Freezing, Lightning). In that case, you can engage low level enemies.
High lust is handy as fuel for your allies once you got them (Lizzie and Meril) and to trigger flirt scene variations. Again, check the walkthrough.