Because of the variability of the environmental fate of this chemical, which shows different decay/leaching rates in different soil textures/environments, you cannot get a direct answer such as "This product will have dissipated in x days".
Studies have shown that acidic soil will not bind with Copper(II) sulfate near as much as soils that are closer to neutral (30% of copper was bound at pH 3.9 and 99% of copper was bound at pH 6.6.). Also, higher calcium ion levels will increase the chemical binding, whereas sodium ions will cause more leaching. Soils that stay moist will retain the copper sulfate. Also, the smaller the soil particles, the more likely for the chemical to stay in the soil.
Also, from Cornell:
Copper sulfate is: (a) partly washed down to lower soil levels by water percolating through the ground, called groundwater; (b) partly bound to soil components; and (c) partly changed into different metabolites, or breakdown products. Copper is considered to be among the more mobile of the heavy metals in surface environments. Copper is bound, or adsorbed, to organic materials, and to clay and mineral surfaces. The degree of copper adsorption to soils depends on the level of acidity or alkalinity of the soil. The distance that it can travel in soil is limited by its strong adsorption to many types of surfaces. All applied copper will become a part of the soil copper content. Although copper sulfate is highly water soluble-that is, it dissolves very easily in water-the copper ions are strongly adsorbed or precipitated to soil particles when it is applied to soil. The leaching potential of this material is low in all but sandy soils.
You said you have the treated roots removed for the most part. Once the chemical is adsorbed to soil particles it will not be an active phytotoxin and you can plant. I personally do not recommend the use of this as an herbicide in areas where you intend to revegetate in a short time frame. And what does leach into the groundwater could travel into waterways where it is a fish toxin. Small amounts like you probably used, especially on high ground, probably won't be a problem, but there are safer and more specialized herbicides available today, such as a combination of 2,4-dichlorophenoxyacetic acid, 3,5,6-trichloro-2-pyridinyloxyacetic acid, and RS)-2-(4-Methyl-5-oxo-4-propan-2-yl-1H-imidazol-2-yl)pyridine-3-carboxylic acid (in ether solution).