Is it okay to submit the revised manuscript well before the due date?
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.)