Think of it like fertilizer. It gives a big boost initially and then the effects fade as time goes on.
I personally put it in when I till and occasionally put a bit more around roots part way through the growing cycle. As I have multiple seasonal garden areas and projects I continue to use...
It depends on how you want to use them. I personally mix them in with my compost and let them decompose a little bit. At least until the point where the shavings are just starting to fade in to the soil. Depending on how much I throw in my pile that can be a week to a month. But your wanting...