Suggested Standing Animation Design
Ideally, a standing animation would be looped, and have enough unique frames to fill exactly 20 seconds, no more, no less.
Animation overrider authors discovered that avatars could appear much more lifelike by playing short animations, in random order, rather than longer, cyclical, animations.
Most animation overriders default to 20 seconds between swapping randomly selected stands.
Since animations can't be cut off in the middle by being stopped early, animations longer than 20 seconds will play correctly. Animations shorter than 20 seconds will play correctly so long as they are looped. The loop body will repeat to fill the time. Unlooped 20 second animations would cause problems for anyone that set their animation overrider to swap stands at a interval longer than the default. Thus all standing animations should be looped.
If your animation's length, without repeating the loop body, is at least 20 seconds there will be no visible repetition while your animation is played by an animation overrider with the swapping interval set to default. So you don't want your animation to have less than 20 seconds of unique frames.
The shorter the animation, the less noticeable it will be as a sequence. Therefore you don't want your animation to have more than 20 seconds of unique frames.