When do I start feeling the effects of Botox?

I am looking into getting Botox for the first time, and my biggest question is about its effectiveness. I would like to know if changes are visible immediately after the procedure, or if it takes a few days to feel the effects. My jaw muscles are a bit on the more developed side, so I am hoping for just a natural refinement of my facial contours; would Botox be sufficient to satisfy this? I have also heard that the effects of Botox vary from person to person, so I am curious if the duration of the results also differs significantly. I would like to hear from those with experience on whether there are cases where additional treatments are needed because the initial effect is weak, or if the results improve over time. I do not want a drastic change and prefer a subtle transformation, so I am also curious about the actual satisfaction levels. I am considering Botox, so I would appreciate your advice.