Search the forum, several similar themed topics.
Check here for some similar ideas;
If its shift change looks like simplest way would be to tag reports and report using tags but expect using actual time is also possible but from experience dealing with times is always more complicated than it first sounds, usually simplicity is easiest so forget am/pm and always use 24hr.
To do larger smaller it needs to be an intiger/number so no :, need plain format like HHmm.