[joejohnson]

When did they buy these oil futures which they were selling throughout the day?

[usefulcat]

It may have been more or less at the same time. Commit to buy X shares at the close; sell X shares now. Or vice versa.

[retube]

A futures "buy" is not an actual buy. Its an agreement to buy at some agreed price at some point in the future. So they entered into agreements to sell during the day, then effectively covered that commitment by entering into agreements to buy at the end of the day.