A thesis defense is really a type of oral examination, and your advisor and committee are the examiners. They can ask questions whenever they want! And it would behoove you to answer them as best you can. As such, it would be wise to prepare your talk with some flexibility, so that even if some time is taken up by questions you can still talk about everything essential, and if there are no questions you don't run out of things to say.
If local custom is that questions be saved until the end, that's fine - but let your advisor/committee enforce that on themselves. If they choose to ask questions in the middle anyway, answer them.
If a question (or line of questions) becomes long and involved, and you are becoming sidetracked, then you could politely suggest resuming the discussion at the end. But let your advisor/committee decide whether they want to do that, or continue discussing that question right then.
If people other than your advisor/committee are present, and you get questions from them, you can answer them briefly if possible; but I would avoid spending a lot of time on their questions. For those folks, you can offer to talk to them further afterwards.