[roryirvine]

In my experience, people do sometimes still use am/pm for whole hour times ("4pm"), especially in informal writing.

But it would be beyond bizarre to write "3:59 pm"

[abanana]

"Beyond bizarre"? Why? "3:59pm" (and 7:30pm, regarding the post above) is exactly what's usually written in the UK. Technical use (24-hour) is different from the standard use used by the general population.