The EEOC process varies wildly from office to office, but you can be confident that it will take at least 180 days and probably longer.
In terms of first contact after you file a charge, some offices will contact you within a few weeks, but others, including my local office, can take as long as a few months.
The EEOC has at least 180 days to investigate the claim. If it goes past the 180 days, you may wish to contact an employment attorney in Tennessee so you can discuss how you should proceed and what you need to do to preserves any state claims you may have that could be subject to a much shorter statute of limitations and that are not stayed by the filing of your EEOC charge. Also, if any additional acts of retaliation occur, make sure you notify the EEOC to either file an additional charge or amend your charge to include the additional acts.