"As far as [something] goes" means "concerning" or "in regards to". "As long as" is more like a conditional if, "provided that it is like this", that a certain condition is fulfilled. "As long you are all over 21 years old, we can serve you beer and wine." You could say the same thing like, "Concerning the time you'll need…" or "Regarding the time this is going to take…" That person could be talking about different aspects of this visit: parking, lunch, accomodations, the time it will take etc. These two sentences concern the time. Another aspect could be, "As far as our return visit is concerned, we can meet on Skype next week to discuss it."

'As far as ..... goes' is often used simply to introduce a new subject. It means 'And now I'm going to talk about the amount of time you'll need'. Or simply 'And about the amount of time ...' You don't need to analyse the individual words within the phrase. Just accept it as a 'set phrase' to indicate the topic of the sentence which follows.

"As far as the amount of time you'll need goes" This phrase tells us an important thing. It tells us that the person is responding to a question or information that was talked about before now. For example, someone asked, "How much time do I need for the visit?" So, the writer here is referencing that question in the response. "As far as X goes" is a set phrase that you can use in response to a question, where X is the topic of the question.

It means 'regarding the amount of time you will need'.