potm
today = potm(days_today); /* 30 December 23:59:59 */
tomorrow = potm(days_tomorrow); /* 31 December 00:00:01 */
today = potm(days_today);
tomorrow = potm(days_tomorrow);
before = potm(p1);
after = potm(p2);
static double potm(double onday);
today = potm(days);
tomorrow = potm(days + 1);
static double potm(double);