Yeah, you need a microscope in order to look at the trichomes for ripeness. I'll take a guess and say at least two weeks, but perhaps three weeks until they're ready for harvest.
Wow, great buds for only 3 weeks into flowering! Expect those buds to pack on a lot more weight before they are done. Most strains take at least 8-12 weeks, some longer.
It is well worth the money to invest in one of those little microscopes that Manels1111 suggested--there is really no other way to tell if the plant is ready other than checking the trichs.
While your buying the scope buy a grow book and read up on harvesting/drying and curing. get yourself some glass mason jars the large ones since your buds are going to be massive. Dont forget the last 2wks before you give um the chop. Flush your soil with plan ph balanced water to get all the nutrient salts out. and the last 8-12hrs before you cut dont give any water it helps with the drying.