Dunn leaves for the United States on Monday, rather than on July 12, to fill a gap left by injuries to prominent drivers available to The Meadowlands stable of Chris Ryder.
Dunn is aiming to gain experience in the US as a lead-up to the world driving championship next month.
Dunn has the chance to improve his record tally of 218 wins this season with opportunities at the Marlborough meeting today and Sunday and Auckland tonight.
Dunn was unsure last night if he would be able to fulfil his Auckland engagements due to flight disruptions from volcanic ash.
"I will just have to see what happens," Dunn said. He is due to fly from Blenheim.
JB Maguire is a top prospect for Dunn in the Marlborough Winter Cup Prelude today and the Cup on Sunday. The 3yr-old has won five of his 11 starts since he started racing in October. JB Maguire mastered a standing start in his most recent appearance at Ashburton on June 6. His other 10 races have been from the mobile gate.
His barrier draw of one is a reservation about his chance today.
JB Maguire is trained by Dunn's employer, Cran Dalgety. Dunn and Dalgety combined to win the Marlborough Winter Cup last year with About Ambition, who was the beaten favourite on the first day after leaving his gait at the start and during the running.
The Dunn-Dalgety combination won the 2008 Marlborough Winter Cup and Prelude with the 3yr-old Bettor's Strike, a son of Bettor's Delight, the sire of JB Maguire.
Dalgety also won both races with the 3yr-old Scorching, driven by Mark Jones, in 2003.
Dunn drives Blackjacky (race 5) and Piper Heidsieck (race 8).
Both horses have been regular drives of his brother, John.
John has opted for Mo Hahn, whom he drove to win on the first day of the Nelson meeting and Valiant Sue, whom he drove to win at Addington two starts back. Blackjacky and Valiant Sue are both trained by Peter Bagrie.
The Robert Dunn-trained Piper Heidsieck has not raced since he cleared maiden ranks at Waikouaiti in February.
Dunn is on the Dalgety-trained Big Picture at Alexandra Park. The 3yr-old won there last Friday when having his first start to give Dalgety win number 81 for the season.
Dalgety is second in the premiership to Mark Purdon and Grant Payne, who have won 100 races in New Zealand.
