You are looking for the ability on the Investment or Idea object to make this start and finish fields as required. Do we have an options to accomplish this in both Studio and Blueprint for MUX?
16.x
For Classic for these 2 required you would need to follow below steps:
1. Administration->Studio->Idea object and then ckick on Views tab.
2. Then go to Fields (screenshot below) and you can find both start and finish dates and make them required.
For MUX:
1. Go to Administration->Blueprints
2. Add Business Rule to the Idea blueprint as below