What is the difference between 'How long does it take?' and 'How long does that take?'
I'm really confused.
They are mostly used in the same way. A slight difference is that there is a little more emphasis involved with 'that'. Then for most cases, "it" is used to address a single object,
We watched the stars at night. It was fun. (watching the stars at night was fun)
whereas, "that" can be used to address multiple things (not necessarily), or a group of things.
We went to the observatory and watched the stars. That was wonderful. (The trip to the observatory and watching the stars were both wonderful)
There are sentences where you cannot use "that", for example,
It was great running into you today.
Coming to your sentence,
- 'How long does it take?'
- 'How long does that take?'
You could ask someone :
'How long would it take for you to drive all the way here?'
'You'll have to drive all the way here. How long would that take?'.
Typically 'that' requires a point of reference. An event or an object, and that's mainly the reason why it is added to the second part of a sentence.
I go to office by bus. How long does it/that take?
I think there's no difference in meaning; you can use either it or that to refer to something that has already been mentioned. However, the use of "that" is emphatic in this context.
Besides, you usually use "it" as an empty subject in a sentence as follows:
How long does it take to go to office by bus?
Use "that" when you are referring to something that has already been mentioned:
"I need to change the oil in my car. How long does that take?"
Use "it" in the other case:
"How long does it take to change the oil in my car?"
In some cases they can be used interchangeably, and they are certainly flexible with poetic license, but you should always be right if you think about it this way.