Well, the way I see it...
Invisibility
could get it's long duration by being so incredibly passive.
It doesn't transport you, provide any info at all, cause damage, cause an effect on others, etc.
Following RM "rules for spells," It maintains a natural progression of escalating power levels based on skill ranks.
At low levels, there is even a decent chance someone will notice your distortion, especially when you move. There have been enough Predator movies for us all to picture this distortion.
24 hrs is still a long time.
While I'm not arguing that we have "invisibility" in real life, we are getting really close!
In the US, scientists have been able to get microwaves to bend around a device (2-d tabletop) with minimal distortion and IIRC, Stuttgart has done something similar with infra-red!
Of course if you 'Tube "invisibility cloaks", you'll find some neat TV fabrics that come close.