Hi, whether "at that time" is needed depends upon on what the role of 'as' is in the sentence.
Do you mean that it would take you two hours to reach home by some
other form of public transport, so that's why you usually take a cab?
If so, then you really need to add an extra word or two to the sentence, e.g.
I usually take a cab home when I leave the office after 10 pm, otherwise it takes me around 2 hours to reach home at that time.