In addition to influencing the design through the Strut Density the Shape Quality can be selected. You can decide whether only a "Preview", a "Balanced" or a "Fine Tune" optimization up to the printable design should take place.
In most cases, a "Preview" only takes a few minutes and gives an overview of the weight and stress development that an optimization can achieve under the given boundary conditions. It can be seen where the flow of forces is located and therefore material is needed. Here it can be checked whether a load/event has been forgotten and where the design reaches the design space limits. This result is not a finished calcultion and does not consider the defined stress goal yet. Is is a very fast, first shot at the optimization and can be used to check the boundary conditions and the ratio of the load constraints to the stress goal.
The "Balanced" optimization can take up to a few hours, depending on the boundary conditions, number of events and the complexity of the model. It provides a detailed/high resolution design proposal. The stress optimization goal is considered fully. More about stresses during the optimization here.
The "Fine Tune" option takes the longest time and calculates a few more iterations on the highest resolution level. Because of this it takes more time in order to obtain a good printable surface and detailed structure of the result. The surface developes the most in these iterations.