one method is to set another keyfram wih the same values.

 

so frame 1 - pose 1

frame    60 - pose 1

frame 90 - pose 2

 

that ill have the figure hold the pose for 2 secconds (60fps) and then change in one second to pose 2.

You can use spline interpolation for the whole thing but do a break spline at frames 60 and 90 to make the change crisp.