11 Numbers and dates
11.3 Times of day
The formulation of times of day is a matter of editorial style, and different forms are more or less appropriate to particular contexts. It is customary to use words, without hyphens, to refer to whole hours and to fractions of an hour:
half past four
a quarter to four
Use figures when minutes are to be included: 4.30 p.m. For a round hour, it is not necessary to include a decimal point and two zeros: prefer 4 p.m. to 4.00 p.m. In British English use a period, but omit the period if a further decimal is included: for example, 0800.02 hours. In North America, Scandinavia, and elsewhere, the period is replaced by a colon: 4:30 p.m.