How long does it take for the periodontist to complete a molar tooth extraction with a bone graft and stitches?

Not long. Most appointments last about an hour including sedation, anesthesia, the procedure, and dismissal. Many like to say how fast they can do things, but anyone can do fast. Quality and the protection, and preservation of the remaining tissue is most important. You will have to live with the results, so make sure to find someone focused on quality, and who will take their time!
Depends. Periodontist and oral surgeons can perform these procedures. I have performed these procedures from as quick as 10 min to as long as 30 min. It really depends if the patient is a compliant patient and there are no other health issue that may complicate the surgery.
10 minutes. Typically oral surgeons can do this quickly and easily as they do it every day. Often instead of grafting they can place an implant in the socket which the process and reduces cost. I schedule these surgeries for 10 minutes plus time for local anesthesia if the patient will be awake. This includes the implant. I do lots of them, close to 1000 per year so i may be a little faster than some.
A nice hour. Every situation is different. Is the tooth hard to extract? Are you hard to numb? In general...Using myself as an example...It took about 1 hour to do my extraction, graft and sutures. I'm sure yours won't be too different unles you are talking about multiple sites.
About 1-2 hrs. It depends on the health of the patient, the location and complexity of the extraction, the volume of bone missing, whether or not a membrane is used, whether you want to be awake or asleep, etc, but in general your appt will be 1-2 hours long overall. Call your periodontist to confirm.