To tell time when a new hour is struck, the format is HOUR + "/dim/" + "\jung\" This literally is referring to the points on the clock. Each hour is considered one point. For this reason, the "2" in "2 o'clock" is replaced with "a couple" as happens with all things being counted in Cantonese
chat /dim/ \jung\ /maahn/ /seuhng/ = 7 o' clock in the evening
Note that the time "morning", "afternoon" or "evening" can come before or after the time. If time comes first, the time is the general term and "morning, afternoon, evening" specifies whether it is am or pm. If times comes last, it is specifying what time in the morning, afternoon, or evening exactly.
Hours and Minutes
To tell time when the time is not on the hour, there are two ways. Cantonese people tend to round the minute to the nearest five. This allows them to use the minute hand of the clock to specify the time. Instead of saying how many minutes, they give the number the big hand points to. The one exception to this is when the big hand points to "6" in which case they specify "half" (bun).
Note that /gei/ can either be used to make a question (meaning "how many") or it can be used in a statement to mean "however many". In telling time it can be used as in "5: what?" showing that the speaker is asking for an exact time. Or it can be used to as in "5: something" meaning "sometime after five".
yat (1) dim saam (3) jou seuhng = 1:15 in the morning
The second way is to read out the entire number for the minutes and then add the term "minutes" before stating morning, afternoon, or evening. This is the way time is expressed in written Chinese and it is used when giving an exact time is important. One additional difference between the first and second methods is that you must read the initial zero when giving the full minutes if it is 9 or less.
sei /dim/ yih sahp -yat- \fan\ \hah\ ng = 4:21 in the afternoon
Generally, Cantonese speakers will shorten \fan\ \jung\ to \fan\. when using this pattern, it is important to say \fan\ after the minutes, otherwise it can be confusing as to which form you are using.