So you input a velocity?  I find it simpler to leave the End Time at 1.0 s and enter the final Displacement in mm that I want to go to.  I often set the Inital and Minimum Substeps to 100 and the Maximum Substeps to 1000 so that I get at least 100 points along the curve between zero load and the maximum load.

Under Analysis Settings, make sure Large Deflection is set to On.