If I recall correctly USCIS checks 2 things regarding income tax for applicants.
- have all applicable years been filed, if not is there a valid reason for that (for instance you have filed an extension).
- Have all owed taxes been payed. If there are any back taxes/fines owed to the IRS, is there a record of these taxes/fines being payed (the payment plan).
The actual wording was way more legal but I think that was what it boiled down to. If this is still the case, your RFE could be cleared by the new payment plan.
To cover your rear, I suggest maintaining all records of the new payment plan. This include phone logs (times + name of person you talked to), emails, screen shots of your online account showing the plan is in place.
As for how long this will take, that's anyone's guess. could be a few weeks, could be several months.