How soon can I get touch up on Botox to masseter muscles?

Effects from Botox can take
months to slowly become visible. Since you've already received an
appropriate dose, it's probably best to wait a month before following up
with your provider.

The masseter is a large muscle. Results of Botox to this muscle can take up to 4 weeks. Often, multiple treatment sessions are needed to achieve the desired results. I would follow up with your physician 4 weeks after your second session. If more is needed then it can be given at that time after an evaluation. Best of luck.

Botox can be used to help reduce the size of the masseter muscles and for people who clench.  If you feel that the muscle is soft, that means the Botox is working and the muscle is not contracting.  The longer that the muscle remains weakened, the more it will reduce in size.  It may take longer to see the reduction in size than to feel the muscle soften.  

I would definetely wait for another 4-6 weeks. Most of my patients reach the peak of masseter reshaping after the second month. 25 U is a safe dose to start and since you had a repeat injection I would give it more time. The best way to assess the changes (since they are gradual) is comparing before and after images.

I think that there is a misperception among patients.  Muscle atrophy does not happen with one set of injections. It will take several treatments every 3-4 months to see any change.  One time injection will not.

I would recommend waiting at this point. It seems like you are getting the desired effect. It will take some time for the muscles to adapt to the Botox and shrink so you might see further improvement over time. Always best to see your injecting doctor in person.