I haven't seen anything specific from the IRS.
The actual notice of the postponement is found HERE
It includes this statement:
"The relief provided in this section III is available solely with respect to Federal income tax payments (including payments of tax on self-employment income) and Federal income tax returns due on April 15, 2020, in respect of an Affected Taxpayerâ€™s 2019 taxable year, and Federal estimated income tax payments (including payments of tax on self-employment income) due on April 15, 2020, for an Affected Taxpayerâ€™s 2020 taxable year. No extension is provided in this notice for the payment or deposit of any other type of Federal tax, or for the filing of any Federal information return."
I have seen a few statements that the deadline is the filing deadline for the tax year. The statement quoted above, though, gives me concern. I'd want a positive statement from the IRS before accepting a 2019 IRA deposit after April 15.