Most of what we use is analine water soluble dyes. These are quite resistant to fading. They make fiber-reactive dyes which work well at room temp. They are quite stable to light, maybe more so than analine dyes. Three days is good for 0.0010 to 0.0015 inch strips.
Thicker strips require longer soaking times.
Don't reuse the dyes. As the dye penetrates the wood the concentration is going down. Also, bacteria and fungi like to grow in the dye, especially after wood had been soaking in it. We have found that both dyes will work at room temp. Just be patient and allow the dye to penetrate fully.