Sorry I haven't posted sooner. I've been so busy this past two days with holiday gatherings and therapy visits.... so glad that's done!
It is impressive Uni being able to leave the treat alone on her nose, shows great restraint and is considered advance training. The 10 seconds wait is we do to ensure fingers don't get snapped off. More than likely, dogs will go for the treat as soon as you let go ...like a hair trigger mouse trap effect.
Can Uni catch treat being thrown towards her? If not, this may be what she needs to learn/practice. You want to get her to where she can catch a treat being released above her.
https://youtu.be/xTyP_fnnP9A
I'm going to steal your "hold it" command to replace "Leave it".... it makes more sense. Plus, it has been confusing for Guinness because the command "leave it" means to turn away, you can't have it, ever.