Photo: Apple Inc.

Several analysts waited until Monday morning — the same day Apple AAPL is scheduled to release its quarterly earnings report — to send clients their estimates of the company’s unit sales (see here). But Piper Jaffray’s Gene Munster waited longest of all.

Munster released a note at 1:54 p.m. Eastern — about two and a half hours before Apple’s results are due to hit the wires — with his latest estimates for Mac and iPod sales.

He was waiting for data from the NPD Group, which surveys U.S. retail outlets and reports sales of a variety of goods — including electronics — on a monthly basis.

According to Munster, NPD data for the past three months show domestic Mac sales up 13% year over year, which implies unit sales of 2.85 million to 2.9 million. Factoring in international markets, however, Munster suggests that total Mac sales probably grew somewhere between 9% and 11% year to year — roughly double the 5% growth the Street is expecting.

The news for iPods was not quite so encouraging.

Munster’s analysis of NPD data for the quarter shows iPod sales down 19% year to year. That suggests unit sales between 9 million and 9.5 million, somewhat below the Street consensus of 10 million. With iPods sales growing faster overseas than they are in the United States, Munster expects Apple to report iPod numbers somewhere in between the Street’s 10 million consensus and the 9-9.5 million implied by NPD’s data.

Munster thinks Apple will confound the naysayers and once again report a strong quarter driven by impressive Mac and iPhone sales. But he has not changed his earnings estimate ($1.37 per share, slightly below the Street’s $1.42) or his price target ($235).

[Follow Philip Elmer-DeWitt on Twitter @philiped]