The new Sage Advice from Wizards of the Coast came out today, and they noted something about spell preparation I dislike.
Can spellcasters prepare spells not all at once, but prepare spells at various times in the day? You prepare your list of spells only at the end of a long rest. You can’t prepare some spells at the end of the rest and then prepare more later.This seems needlessly strict, and I don't know that there's any good in game reason for it. Sure, for clerics you can say that their deity wants prayers at dawn, or midnight, but that seems awfully small minded for most gods, and doesn't make sense for wizards. So here's the house rule:
Can spellcasters prepare spells not all at once, but prepare spells at various times in the day? Yes. During the day, a spellcaster can use a short rest to prepare new spells in slots she has available.That should provide some flexibility, while the hour rest requirement prevents it from being misused. In my experience in 3rd edition, it was rare you wanted to leave a slot open in any case, so I'm not too worried about abuse.