How long does the effect of square jaw Botox last?

My jaw joint feels stiff every time I wake up in the morning, and lately, when I look in the mirror, my jawline seems a bit more uneven and wider. I have a habit of clenching my teeth while sleeping, so it feels like my jaw muscles are gradually developing. I am seriously considering getting square jaw Botox.

However, I'm hesitant because I've heard that the effects of Botox wear off quickly if you miss a treatment cycle. Typically, when do the effects appear and how long do they last after getting square jaw Botox? I'm also curious whether I should choose a domestic or imported product to ensure the effects last longer without worrying about developing resistance. If anyone has seen definite slimming results, please share some product recommendations or tips!