The idea of this concept is simple, when you create your character the devs would allow you to pick a month and day. Various months would provide your character access to an ability in the form of a daily use. You can use this spell at 1 + [PC lvl /2]. These spells would not recover with short or long rests. The way these spells would work would be of the real life calendar or real life clock time. This concept is similar to how Dragon Age Inquisition did their war table.
The Months
For the names of the months i turned to BG1-2 Wiki. They named them the following:
--> Hammer, Alturiak, Ches, Tarsakh, Mirtul, Kythorn, Flamerule, Eleasias, Eleint, Marpenoth, Uktar, and Nightal
Given Spells/ Abilities
1) Control Water: ice runs in your veins, for you are born in the winter. [Combos with create water- deal 1d3 dmg to enemies around the water every round].
2) Long strider: your born on the coldest month of the year, your resolute and firm. None shall stand in your advances.
3) Goodberry: like the waking season, your will is stoic and unyielding. Nature is your will, and makes a boon of fruit on a daily basis.
4) Minor Haste: your mind is racing like a thundering storm, child of the wind and lightning. [+10 movement range]
5) Minor Regenerate: few are as calm and tranquil as you, this allows you to heal your wounds- as stress is a word you do not know. [heal 1d10 over 45 sec]
6) Speak with Plants: human friends are for the corrupt and the infirm. The plants and flowers where before, and shall be after. I chose wisely.
7) Animal Friendship: those born in the summer awaken with the new born animals. Your souls are one and the same, and you have no intention to hide it.
8) See invisibility: the sun burns away all lies and illusion, your born in its month and share in its eternal glory. None can hide, for your will burns like the sun.
9) True Strike: Born of strife, the uncontrollable screeching of territorial beasts tempered you through your womb. Your ferocity is that of a beast.
10) Identify: as the leaves fall, many begin to starve and famish. Your a survivor, and a scavenger. Your talent is rare, and you know it.
11) Power Word kill: Your born in the dusk, life falls and nature rots. Only those willing to fight will not die. Your will is your sword- move or fall.
12) Augury: concerns and doubt are born when a new year approaches, blessed by a spirit your an oracle, your visions are truth, and your words inspire or terrorize.
The above is a lot of homebrew obviously, and the spells are roughly based on the names of the months. There is a lot of room for a fun discussion on what abilities people would want to see or think would work better. Have fun. Lets see what we can come up with.