Will brows start to regain movement after Botox after 3 months or does it slowly happen beginning at 2 weeks?

Botox usually lasts 3-4 months, although some patients due metabolize it quicker. You'll start to notice movement and improvement before your 3 month mark

At two weeks Botox is fully set in. Very slowly over the next few months, movement will return. This is good news for people like you who have not achieved the results they expected. Most importantly, return to the clinic where the treatment was done. The injector needs to see the unfavorable results so the next treatment can be modified to meet your goals.

They won't start rising at 2 weeks out, but you should start seeing some slow improvement before a full three months' time. The full effects will take 3-4 months to go away, but you should start seeing some improvement at 1.5-2 months out. When people have ptosis (hooding) already, it's very important to go much higher in the forehead with the injections, or the hooding worsens. It will resolve, but it will take time. "This answer has been solicited without seeing this patient and cannot
be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."