When you have submitted enough FP for the tech to move to the 'Unlock' stage, it automatically moves on. If you delay unlocking it then, you just need to click on the tech to get the same window to open and it'll have the option to unlock available.
It would be problematic if the tech just unlocked itself when you have the requirements, since some quests require you to finish a tech, and some people wait for quests like those before they unlock them so the quest isn't kept in waiting.