C = rem (A, B) returns the remainder left after dividing A by B, as a duration array of the size the two broadcast to. At least one of A and B must be a duration; the other may be a duration or a numeric array, which is read as a number of days, the unit a duration counts in.

The result takes its sign from A, where mod takes it from B: the two agree only where the operands share a sign. A remainder by a zero duration is NaN, where mod gives A itself. The display format is taken from whichever operand is a duration, or from A when both are.

Source Code: duration