This came from the IRS website.
Can I file my return electronically even though I am filing a Form 8379, Injured Spouse Allocation?
Yes, you can file Form 8379 electronically with your tax return.
If you file Form 8379 with a joint return electronically, the time needed to process it is about 11 weeks.
If you file Form 8379 with a joint return on paper, the time needed is about 14 weeks.
If you file Form 8379 by itself after a joint return has already been processed, the time needed is about 8 weeks.