Hello, so a pretty simple suggestion.
Currently, Dark Invocation: Sage Tongues is a once-per-rest ability. Seeing as you can rest every 30 minutes regardless of your rest meter, my suggestion is to add a 30-minute timer to Dark Invocation: Sage Tongues. Else those that use it are just resting and re-casting it. It'd be a simple QoL change that wouldn't have any great mechanical impact, I believe.