Fridays, Saturdays, and Sundays are no-nos (Stoned, Dead, and Eradicated). The other days (Monday-Thursday) are +1, +2, +3, and +4, depenting upon the week of the month used, to the number of points applied to the particular stat. I could be very wrong here as it has been a long time since I used those lamps (I don't normally mess with them)I beleive, but am not sure that the progression follows pretty closly to the stat list, i.e. January=MGT, February=INT, etc.
I can't remember the stats for August-December except that one of them is skill points and one is Food.