If the person behind me is davening a long S”E, and I need to leave, am I required to wait for him to finish before stepping back, even if he is davening for half an hour and I will be late to work, or can I step back into his daled amos after a certain point?
There is a machlokes what is considered walking “in front” of a person davening. Some poskim say it means the front and all the sides that he can see. However other say it means only directly in front of the person. The Mishnah Berura says that when there is a need we may rely on this opinion. Your case definitely is a need. Therefore my advice to you is to make sure you position yourself in a place that you are at least not directly in front, or in a place that you will have to cross in front of the person who davens such long S”E. It would also help to mention this to him so that he can stand S”E in a way that won’t hinder you.
M”B 102- 15.