What’s the maximum amount of frames YOU think an idle animation should have? Will it affect memory usage?
If you are having a problem with memory usage, then worry about the number of frames in an animation. If you aren’t, then don’t.
Trying to solve problems that don’t exist will not help anything.
I would make 7 or 8, 1-2 second long idle animations, and then randomly blend between them/add them.
+1 for sdfgeoff
What Sdfgeoff said.
How idle animations should be handled in best efficiency is you have multiple simple idle animations which you randomly play when your character is in idle state. You can observe this mechanic in practically every video game that has idle animations.
Also note that animation length doesn’t correlate to memory usage. What it depends on is how many keyframes you actually have for how many bones.