Use 2pm, 3.30am (closed up) in a web context

Use 2 p.m. and 3.30 a.m. in official documents

Note: noon is 12pm, midnight is 12am. It may be clearer to say "noon" or "midnight"

Note: To configure the correct date format on a Drupal site, go to admin/config/regional/date-time/formats/40/edit. 

The PHP code you need to add in the Format string box is "j M Y, g.ia"