Machar Chodesh

What is the connection between the haftarah of Machar Chodesh and the day itself? Besides the fact that the fourth and fifth words of it are "Machar Chodesh"?

Malchus Beis David is often symbolized by the lunar cycle. If one counts from Avraham, the fifteenth generation is Shlomo, representing the zenith of the dynasty, while the thirtieth generation is Yoshiyahu, who was the last independent king from the dynasty (as Yehoachaz and Yehoyakim were respectively deposed by and subservient to Egypt, and Yehoyachin and Tzidkiyahu were the same by and to Bavel). Erev Rosh Chodesh is the darkest period of the month, as it is the day before the first sliver of the new moon appears. This haftarah discusses where David's life reached a nadir, as, where he had previously been the king's musician, hero, and son-in-law, he was now reduced to a fugitive fleeing for his life from a murderous king. Hence, it accurately describes the beginning of David's own "Erev Rosh Chodesh", which lasted until the death of Sha'ul and his own coronation.

When I told this idea over at a meal this past Shabbos, a friend of mine suggested that one could also view the beginning of the haftarah as being an "Erev Rosh Chodesh" of a much shorter duration, as David's absolute lowest point, before things began to improve, was truly in the beginning of the haftarah, where he may have even had doubts as to how much his best friend would be willing to help him by going against his father's wishes. This darkest moment ended by the end of the haftarah, when Yonasan made clear to David the extent to which he would go for him, and the rest of I Shmuel describes the rise of David's star.