
I see a lot of confusion about when to spell out the time of day and when to show it as numerals. The rules are pretty simple. You want to spell out times of day if they are in even, half, or quarter hours: “She left at seven o’clock and returned at seven fifteen.” If you want to stipulate a time of day that doesn’t follow this rule, use the numerals: “He looked at the clock and it read 6:18.”
Now, if you really want to emphasize an exact time, you can use numerals even with times that normally would be spelled out: “The store opens at exactly 8:30.”
As far as dates go, just use the numeral and don’t make it an ordinal: “He’s coming on December 5” (not December 5th). Or spell out “fifth.” If you are not mentioning the month with the day, you spell out the day: “She should be here on the sixteenth.”