Is mutual masturbation safe immediately after tummy tuck with muscle repair?

This is not an unreasonable question, and the straight up answer is NO.
Immediately after a tummy tuck, there is always the chance of bleeding secondary to increased blood pressure which occurs with both sexual excitation and orgasm.  Muscle repair is 100% healed at 6 months, 90% healed at 3 months, and 75% healed at 6 weeks.  Therefore, if you were my patient, I would not recommend sexual activity of any kind prior to 6 weeks.  
The spasmodic movements some people have during the crescendo of sexual excitation and the accelerated movements during orgasm can, at times, cause shearing forces between the rectus abdominus and the skin and subcutaneous tissue above leading to a potential space which might be filled with a seroma or hematoma.
Once you have chosen one of the excellent Board Certified plastic surgeons in Dallas, you should pose this very reasonable question to him or her and get their medical advice.

Thank you for sharing your question and congratulations on your tummy tuck.  I would avoid masturbation for at least two weeks after surgery as the stimulation will cause your blood pressure to rise and your heart rate to quicken.  These symptoms can lead to an increased risk of bleeding that should be avoided.  Hope this helps.

Your surgeon is the best one to answer this question as he/she is most familiar with the details of your surgery and how you've been progressing through recovery. In most cases you will want to wait a few weeks after surgery before resuming sexual activities.

I would say that you probably need to wait 3-6 weeks before considering this.  You also need to limit your exertion early on as well.  You are best to review with your doc.

Congratulations on having undergone the tummy tuck procedure.  Your plastic surgeon will be your best resource when it comes to specific information/advice. He/she knows exactly what was done and how you are progressing. Concerns would include an increase in heart rate and the potential for bleeding. Muscle spasm may be painful. Obviously, significant pressure on the surgical site is not a good idea either. It is not uncommon for patients to report increased swelling that occurs after vigorous exercise (including sexual activity), even several months after tummy tuck surgery. 
 I hope this helps.

The simple answer for this question is no. I tell our patients to keep their heart rate and blood pressure is normal for the first two weeks after surgery. This will decrease the incidence of postoperative bleeding in my period. Any  activity that puts a strain on the abdominal repair this early after the surgery, maybe risking a loosening of the repair. I would highly recommend  that you ask your operating plastic surgeon for their thoughts on this question. Congratulations on your surgery.