The USPTO is a stickler for being on time. In the event that the Trademark examiner issues an office action, the applicant must submit a response to the office action, accounting for ALL of the stated legal issues, within six months of the issuance of the action. In Office Actions that raise both procedural and substantive issues, this can be particularly confusing. Please discuss each issue carefully with a trademark lawyer to get a sense of the scope of the response needed and how much preparation will be required to draft and submit the response.
The USPTO is not entirely unforgiving and if you happen to miss the 6-month period, you may be able to request an extension of time to submit your response. You can expect the USPTO to charge an extra fee for granting this time allowance.