Xaelvaen
Stuck in the 90s
My House Rule on this issue:
For all (save at end of turn) mechanics that otherwise end the spell, I allow the caster to invoke disadvantage on the save once per creature affected. The caster chooses when that disadvantage applies, giving them the power (and thus intellectual decision-making) of risk/reward.
So, a caster who -really- wants that spell to stick immediately, can use it on the first save, and ensure that the creature is affected at least one round. A caster who is more interested in a long-term effect, can save that disadvantage to be used on the second round or later.
In any event, -before- I roll the monster's save, the caster must tell me whether or not they will apply their one disadvantage. I've found it is a good balance between the core concept, and duration-based spells that outright work after a save.
For all (save at end of turn) mechanics that otherwise end the spell, I allow the caster to invoke disadvantage on the save once per creature affected. The caster chooses when that disadvantage applies, giving them the power (and thus intellectual decision-making) of risk/reward.
So, a caster who -really- wants that spell to stick immediately, can use it on the first save, and ensure that the creature is affected at least one round. A caster who is more interested in a long-term effect, can save that disadvantage to be used on the second round or later.
In any event, -before- I roll the monster's save, the caster must tell me whether or not they will apply their one disadvantage. I've found it is a good balance between the core concept, and duration-based spells that outright work after a save.