The time varies, depending on whether you apply electronically or submit a paper Income-Driven Repayment
Plan Request. It may take a few weeks, since the servicer will need to obtain documentation of your income
and family size. If you are currently repaying your loans under a different repayment plan, your loan servicer
may apply a forbearance to your student loan account while processing your request for an income-driven
repayment plan.

For more information go to the Income-Driven Repayment Plans: Frequently Asked Questions Website