Best Case Theory

I still have not read the Official Novel... the 3800 Marks Indicating Days that David has been on Planet 4 is Interesting, i would HOWEVER wonder why he would need to keep a Tally as he is a AI and so he would have a Built In Clock/Calendar and so Marking of Days would not be required for a AI.

But if we are to Assume this is a indication of the Time David had spent on Planet 4 then it would mean that David had Arrived on Planet 4 in what would be Earth Date of Early July 2094

Something to take NOTE is the Crossing which shows Dr Shaw's Hair Growth is something that would take 5-10 Months Depending on Person (Each Persons Hair Grows at Different Rates).   I had discussed this before and Average Growth that she had for a Average Female of her Age would have been 6-8 Months.

So we can assume this indicates that from when Dr Shaw had recovered David's Body/Head to when she had Re-Attached him would have been 6-8 Month Period.

It seems that Planet 4 is in/near the Zeta 2 System, which surely means that the Juggernaught would NOT had taken long to arrive at Planet 4.

So when looking at the 3800 Days that David had been there by the Time the Covenant Crew Arrive, then this would FIT with the expected Hair Growth of Dr Shaw while she was contemplating putting David back together which then would also leave us to Speculate the Journey from LV-223 to Planet 4 could have taken Merely Days... Certainly no more than a Few Weeks.

So it Certainly seems that 7 Months had Transpired from when Dr Shaw had recovered David to when the Covenant Ship had arrived of which we can Assume 5-6 of these was Dr Shaw alone with just David's Head.

I dont think we really have any Exact Dates though... just that about 10 Years 11 Months had past from when Dr Shaw and David had Set Off from LV-223 to when the Covenant Arrived on Planet 4 (End of Prometheus to Events of Covenant).

Speculating what Happened between Both Movies would be Interesting i am drawn to a Certain Period of Events which i could give, but it could be distracting from the OP.  The only Context to the OP would be to Indicate that David had spent a Period of Time between a Good 10 Years, 5 Months in Creating the Xenomorph.