Startup problem in boost converter
You can see there's a "Vramp" in there. This creates a timing element.

If the Vramp is above the first op-amp's signal, the transistor will be off. So if you know, for example, that your error amplifier (the first op-amp) can never output a voltage higher than 3V, you can make the Vramp such that it goes between 0V and 4V, which guarantees that whenever it's above 3V the transistor is always off. In this case that would be a minimum off-time of 25%.