Hi Melissa, here's a Formula that I use in my Dev org (compile size = 756) that we might be able to tweak

IF(
HOUR( TIMEVALUE( LastModifiedDate - ( 4 / 24 ) )) = 0,
"12",
IF(
HOUR( TIMEVALUE(LastModifiedDate - ( 4 / 24 ) )) <= 12,
TEXT(HOUR( TIMEVALUE(LastModifiedDate - ( 4 / 24 ) ))),
TEXT(HOUR( TIMEVALUE(LastModifiedDate - ( 4 / 24 ) )) - 12)))
+":"+
LPAD(TEXT(MINUTE( TIMEVALUE(LastModifiedDate - ( 4 / 24 ) ))),2, "0")
+" "+
IF(
HOUR( TIMEVALUE(LastModifiedDate - ( 4 / 24 ) )) < 12 ,"AM", "PM")