If you filed the Form 8379 by itself after a joint return has been processed by the IRS, then processing will take about 8 weeks.
If you file Form 8379 with your original return, it may take 11 weeks to process an electronically-filed return or 14 weeks if you filed a paper return. More details are here https://www.irs.gov/taxtopics/tc203.html
If it's been longer than the number of weeks mentioned above, you can call the IRS to check the status of it. You can also call the IRS tax refund hotline at 800-829-4477, Monday - Friday, 7:00 a.m. to 11:30 p.m.
