Numerically described periods are not capitalised:
The preferred style is to use numerals rather than text.
Also refer to Time of day.
For time spans, use as few figures as possible and no full points after 'am' and 'pm':
Normally the dash used for time spans is an en rule. For website content, replace the en rule with a hyphen because the en rule does not always display correctly.
Authorised by the Associate Director, Service Delivery & Support
25 October, 2011