On Game Dev Tycoon when one of your employees has their boost ready and you're making a game, is there an ideal time to use it or just as soon as possible (so you can hopefully get 2 during the production of that game)?
According to the wikia:
The boost gives the employee a massive increase in output of either design, technology or training. The output during a project is determined by the current phase of development.
So boosts should be used depending on whether the current phase of the game development will be benefited or not. No point in boosting design in a technology heavy development phase and vice versa.