The amount of time that a spell level lockout should last isn't something for which I have a solid answer. It could work in a manner similar to 4E where the end of an "encounter" resets the lockout on the majority of abilities, but "combat" states in engines is something that, in my experience, is often triggered on/off in weird ways. If a lockout lasts for something like 30 seconds or 45 seconds, that lockout will likely last longer than the remainder of the combat, but not so long that the player would have a compelling incentive to "spam stand", which I agree is bad. Whether the answer is a timed lockout or a combat state-released lockout, I'm not sure.
I think health and hit points can be handled differently because the player always has a high incentive to avoid as much damage as possible for all of their characters. I.e. conserving health is (almost) always in the player's best interest, but conserving spells may not be.