Not going to hi jack the thread but I think you kinda need to study grammar again if you think when and if are like たら and ば. When is not 仮定. Look up what 仮 means. たら here means 未来の確定条件を表すこと. Which is 'when' in English. 確定 and 仮定 are like polar opposites. たら has both functions. No it isn't obvious and no, when is not the equivalent of たら.