AddDays
void AddDays(int32 days);
oneDayAgoStart.Date().AddDays(-1);
twoDaysAgoStart.Date().AddDays(-1);
threeDaysAgoStart.Date().AddDays(-1);
fourDaysAgoStart.Date().AddDays(-1);
fiveDaysAgoStart.Date().AddDays(-1);
oldestAllowedDateTime.Date().AddDays(-fMaxHistoryItemAge);
output.AddDays(date / U_MILLIS_PER_DAY + 0.5);
lastDayInMonthBefore.AddDays(-1);
date.AddDays(7);
date.AddDays(seconds / kSecondsPerDay);