This is a real period of time for which the program calculates the response starting from the moment of the first impact. If you specify a drop height, the solution time does not include the period of the free fall of the body. The program estimates a value for the solution time based on the model geometry and default material properties. The default solution time is based on the time it takes the elastic wave generated by the impact to travel through the model. The program estimates the velocity (Ve) of the elastic wave from:
Ve= (EX/ρ)1/2
Where EX is the modulus of elasticity and ρ is the density. The wave starts propagating in the model at the moment of impact. Assuming that the length of the model is L, the wave takes a time period approximately equal to 2L/Ve to travel to the farthest boundary, get reflected, and travel back to the originating area. Forces that are opposite to gravity start acting on the model during this period. The program sets the default solution time to 3L/Ve. Note that this is just an estimate that should help you enter a reasonable period.
The impact period is usually very small. This is why the program asks for it in microseconds. The maximum response may occur during impact or after while the body is rebounding. The study can evaluate multiple impacts and rebounds if you specify an adequate solution time.
The program gives a warning message if it estimates that solving the problem will take more the 60 minutes.