What's the recommended time between surgical tooth extraction and implant surgery?

Your dentist is concerned that the tooth may be difficult to remove if it crumbles at the time of surgery and wants to make sure the bone is preserved as much as possible.  It is good that currently there are no signs of infection but this can change and if so bone loss could occur.  When your periodontist takes the tooth out he/she can see if the site is compromised or not. Implants are a certain diameter and need to be surrounded by bone so the site needs to be of adequate width.  Sometimes the implant can be placed at the time of surgery however at times it is necessary to rebuild the site with bone graft and other materials.  If this is the case then you may be waiting 3 - 5 months between the time of extraction and implant placement. 

If the tooth is fractured, which
is the most common cause of a post-root canal treated tooth to need to be
extracted, the sooner you have it extracted, the better long term
prognosis. A fractured tooth can lead to infection but it can also be
responsible for loosing bone support around the tooth which will be important
when you have the implant placed. Typically, the extraction would be done
by the same person that does the implant. They can assess the amount of
bone remaining after the extraction and perform the bone graft at the time of
extraction so that healing will be quicker and you can get your implant placed
sooner. Most every periodontist (gum specialist) places implants so it
could be done in the same office by the same dentist. If for some reason
the extraction is going to be done by a different dentist than the one that
places the implant, make sure you tell the periodontist at the time of the
extraction that you are considering an implant in the future so a bone graft is
done at time of extraction. After the extraction, an implant can usually
be placed in 4-6 months, depending upon the amount of bone that remains after
the extraction. My advice is to get the extraction done as soon as
possible and start the healing process.

Good question....that would depend on a number of different factors.  My first question for you is why is the periodontist not placing the implant. Usually when a tooth is extracted and there is no infection a bone graft is placed.  If this is placed it is usually 2-3 months before they would go in and have the implant placed.  Without a bone graft 4-6 weeks is usually enough time.  Good luck.