Time

Always use the 12-hour clock with a full stop between the hours and the minutes (not a colon):

We're going to meet for lunch at 1.30pm.

Don't use additional ".00" for times on the hour, and close up space between the number and the "am" or "pm":

The lecture starts at 4pm.

Use "12 noon" or "midnight" instead of "12am" or "12pm":

All students must leave the bouncy castle before midnight.

Periods of time

Use an en dash to link up time periods, and shorten figures where it's possible:

The Second World War (1939-45) was a turning point for the world.

He lived in a van on the driveway 2003-7.

Use slashes (with no spaces) to refer to an academic or financial year:

We attracted more undergraduate students in 2013/14 than we did in 2012/13.

If you're using "from" to start a date or time, always use "to" to end it (and not a dash):

The summer holiday runs from June to September.