Basically how it works is:
The word 'now' is used as a variable and its is basically a functional timer in Minecraft.
So, this code
means it's trying to find the difference between now and the last time you used it, as in this line.
So, you can't get rid of the %player's uuid% part, but a modified way to make the variable shorter is to shorten it to just
{%player's uuid%.lastSneak}


