How long does it take for my voice to get better after straining?

This all depends on how badly you strained your voice. If you pushed your voice and there is no physical damage it can be a few days. If there is damage to the vocal folds it can take anywhere from weeks to months. You then have to make sure you don’t continue to strain because of bad vocal habits. If straining keeps happening, you have to make changes and go to a vocal coach that knows how to work you through to a healthy voice and who helps you keep your voice healthy.  You must be willing to do the work necessary.