Following are the factors that impact test generation time.
Hardware
2. Model constructs
3. Configuration of test generation
4. Model size/complexity
The larger the test data or model and the more advanced test generation options you use, the longer test generation will take for a given model. The smaller the test data or model and the fewer advanced test generation options are used, the faster test generation will complete
Note that every model is different! Factors such as model structure, logical errors (inability to reach 100% coverage) also influence test generation time.