Is is better to ask:

What time do you finish tomorrow? or Will you finish tomorrow?

As far as I know we can also use present simple to talk about future when it is connected with timetables, schedules.

And what's the difference in meaning?

And the same in this context:

what time do you finish today or will you finish today?

when we have specified working hours always finish at the same time what tense should I use and the other way around when somebody has unspecified working hours what tense is better to use?

Thanks in advance
In AmEng we use the two quite interchangeably.
layla1234What time do you finish tomorrow? or Will you finish tomorrow?
Do you mean this?

What time do you get off work tomorrow?

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It's common to use either the present progressive or future simple tense to talk about the immediate future.

Also, there are speaker who use the present simple to talk about the future, but it often happens in conversations.

In general, your question is a matter of writing style and depends on mood or context.

Therefore, it's quite difficult to provide you one answer that fits all kind of contexts.

It depends on how you view the situation

When you ask somebody what time they will finish tomorrow, you're asking them to give you their best guess about when they will finish

On the toher hand if you ask them what time they finish, the implication is that they are on a fairly rigid schedule tomorrow and the time they finish is pretty much set.

If somebody works on a fixed schedule then I would say that asking, what time do you finsih? would be more natural. On the other hand if they're going to be working on some project tomorrow and they can't be sure about exactly when they will finish then 'will you finish' would be more natural.

Think about this example:

What time do you think you will finish tomorrow?

Imho, you can't change the tense to simple present here

'What time do you think you finish tomorrow?' would sound a bit weird, on the other hand if you ask, 'Do you know what time you finish tomorrow? it sounds ok because here it's implied that you're talking about a set schedule
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 CalifJim's reply was promoted to an answer.