get off' is short for get off work. Instead of saying 'leave', it is much more common (at least in the U.S.) to say 'get off'.
The first example is used when you want to ask about longterm situations.
The second example is used when you want to ask about short-term situations.
'Julie, I want to grab a bite to eat this evening. What time do you get off today?'
get off' は 'get off work'（仕事が終わる）の短縮形です。（少なくてもアメリカでは）'leave' よりも 'get off' の方がはるかに一般的です。
一つ目の例は長期的な状況を尋ねています。
二つ目の例は短期的な状況を尋ねています。
'Julie, I want to grab a bite to eat this evening. What time do you get off today?'
（ジュリー、今晩軽く食事をしたいんだけど、今日は何時に仕事終わる？）
This question implies that the person is leaving from home so it isn't necessary to state it. The person should respond by telling you at what time they leave their house. I hope that this helps! :)
When (What time) do you usually leave home for work?
When (What time) are you leaving for work?
There are several ways to ask the question. Some are less formal than others. Often we start the question with 'When' instead of 'What time'. If you use 'When' then you do not use the word 'time' it is implied in the question. However using 'What time' makes the question more specific and avoids any ambiguity in the question.
When discussing work routines, if you wish to ask someone when they leave home for work, then you can use the abovementioned suggestion.
To set off (for somewhere) = to depart (to somewhere)
いつも何時に家を出て仕事に行っているのか尋ねたいなら、上記の文が使えます。
To set off (for somewhere) = to depart (to somewhere) = 出発する
All three of these questions ask the person what time they leave their home for work. The first two both make use of the verb "leave". The last question uses the verb "head". In this context, it is similar to leave. It is a bit more causal however and gives you some options when speaking to someone.
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