I have searched the internet far and wide in search of an answer but to no prevail. My question is when should I repot my bonsai sprouts?
There's no such thing as bonsai seed, bonsai sprouts, bonsai seedlings or bonsai saplings. They're just seed, sprouts, seedlings and saplings.
First of all: you're not growing a bonsai, you're growing a tree. That tree you are growing to become suitable for bonsai, but still first thing you are doing is growing a tree. Guidelines for growing trees can be easily found.