Which element size is that Time Increment graph for? Do they all end up at 900 s time step or do smaller element sizes have different values of the time increment?
For a specific element size. Run a series of time increment experiments. Change the Initial and Minimum Substeps using this sequence: 1, 2, 4, 8, 16 and see how the Accumulated Plastic Strain changes (you already have the results for 1).
That will be very tedious to setup because you have to do it 13 times to get every Step in the simulation. Please show how the temperature changes over those 13 steps.