How long does masseter Botox take to attach to the nerve therefore stopping further risk of migration?

Your photos are helpful to see your masseters. I would be careful of treating only the TMJ since it could cause less structure in the lower face. If the TMJ causes you pain, I would treat it, but consider a filler/hylaronic acid to fill in the "sulcus" or area around chin. Hope this helped.

Yes, you can have Botox and fillers a day apart. However since you mentioned that the Botox treatment has caused significant changes to the jawline you could consider waiting two weeks for your filler session. At that time your Botox will be in full effect.

Please watch the video below for a detailed answer on how Botox is used safely to treat symptoms of TMJ (Temporo-Mandibular Joint) Disorder

A popular non-surgical procedure to slim or feminize a jaw is masseter Botox. That's botulinum (aka Botox) injected into the masseter muscle along your mandible. This muscle is one of five muscles that helps close your mouth. So the other four will be plenty to keep you chewing, your jaw will...

Taking muscle relaxers at the time of your Botox treatment will not affect the treatment results. It is recommended to avoid blood thinning medications and supplements prior to treatment to minimize risk of bruising.

Heat from your fireplace or grill three weeks after your Botox treatment would not shorten its longevity. It is more likely that you were undertreated for the desired results. You can return to your injector for an evaluation and touch up.