Calculate the time it will take the object to hit the ground using classical physics (hand calc). Divide that number by 10 to begin with. You may want to try it again with 100 steps to hit the ground.
Time step in an explicit analysis is determined very differently than in an implicit analysis. The solution may not remain stable if the critical time step is exceeded. LS Dyna determines this automatically. The user can empt control via the EDCTS command in Ansys. Download the Theory Manual from LSTC.com (LS DYNA website) and read on the subject. It's important to understand the basic concepts in what you're doing.
