Here are some activities for learning your 24 hour times:
Explaining the 24 hour clock
http://lgfl.skoool.co.uk/content/primary/maths/24_hour_time/index.html
Converting 12 hour into 24 hour time:
http://www.higherbebington.wirral.sch.uk/games/24hour.html
The 24 hour clock, tutorial and game
http://www.bgfl.org/custom/resources_ftp/client_ftp/ks2/maths/time/index.htm