I have worked in IT field for 18 years in Australia and I have resolved many DNS related email messaging issues, email blacklisting issues, as well as identifying and resolving root cause of email blacking.
If the job simply involved setup of spf, dkim, dmarc and other dns records, the setup can be done in less than an hour but propagation may take some time to complete.
If the domain name is blacklisted, then it will take a bit more time to delist it.
The completion may range from 2 days (I check and make sure dns propagation is completed successfully) to a week, depending on what the issue(s) is.
Nevertheless, I am offering a fixed price of $30 to help you fixing up your dns for email marketing.