The two series were previously held back-to-back over a fortnight.
The auction house say they will be staging a joint pre-sale exhibition across 10 days using more than 65,000 sq ft of gallery space in York Avenue.
The new scheduling mirrors Christie's approach who, for the first time last year, packed all their auctions in these categories into five days for both their May and November series.
They also held an additional cross-category sale to offer 'curated' works.
Jam-Packed Schedule
Sotheby's have four auctions scheduled to take place in New York between May 9-12 - two Impressionist and Modern sales and two Contemporary art sales - an evening and day event in each case. Christie's are yet to announce the dates of their sales.
Traditionally, the 'big two' auction houses avoid their sale dates clashing but, should Christie's select the same week for their events as expected, the jam-packed schedule may make some degree of overlap unavoidable.
Phillips are holding sales on May 8 and May 10 - the latter event held an hour after Sotheby's Impressionist & Modern Art day sale.
