Is it okay to submit the revised manuscript well before the due date? Recently I received comments from two reviewers on my submitted manuscript as major revision. Both the reviewers have given a few major comments along with some minor comments. The major comments are something like this:


It is essential to analyse. 
Please add some more explanation on this. 
Please discuss with xyz method and check the difference in the results.  
Why didn't you do it?


The due date is 45 days. 

I finished the first 3 major comments in a week. However, I have planned to work on comment number 4 as my future research. I had also mentioned it in the manuscript before submission. But still one reviewer commented as "Why didn't you do it?" So I have explained little more about it (why am I skipping it here) in the revised manuscript. 

Now my question is, can I submit the revised manuscript now? Isn't it very early i.e. 38 days earlier than the due date?

If yes, will it give a bad impression that I have another 6 weeks, still I am skipping comment number 4? 

Note: The reviewer has not told me work on comment number 4. I am also not interested in including it in this manuscript.
Yes, it is fine to submit revisions early.
The timescale doesn't really come into it. Either the revised paper is good enough for publication, or it is not. The logistics of when you carry out the work and how long it takes are entirely up to you. The important thing is that, in your covering letter, you explain in detail why you have chosen not to follow recommendation 4. 

In fact, submitting the revisions early could even benefit you. It will mean that the paper is fresh in the editor's mind, which could mean they are able to make an informed decision more quickly.

Note that if you did want to do number 4, but 45 days was not long enough, it would be very reasonable to contact the editor to explain this and ask for an extension.

(NB I don't quite understand what point 4 is asking, so it's possible there is some subtlety I am missing. This is Okay!! Why didn't you do it? What is "this"/"it" and what is meant by it being "okay"? I presume these are not the exact words that the reviewer used.)