In all roman languages one ask for the hours of the day, not for the time of the day. (Actually the English "What is the time?" is a little bit strange. If we were not accustomed to this question and if we didn't know the meaning we would expect a definition of time to this question. For instance based on the philosophy of Bergson, the French philosopher. In his view time is not a homogenous continuum, but depends on the intensity of the moments. However in English if we asked for a definition of time we would say "What is time". )
In Portuguese we ask for the time with "Que horas são?" what is literally translated "What hours are?" (What is actually strange as well, because que / what asks for properties, not for a quantity. A correct answer to "Que horas são?" would be very nice ones or something like that. There are a lot of people who believe that analyzing linguistic structures has something to do with "logic". These people in general don't have a concrete idea what is "logic" and furthermore they have no clue of linguistics. Actually "Quantas horas são?", "~How many hours are?", would be more "logical".)
For those who speak Spanish: (It is to suppose that a lot of people who learn Portuguese speak Spanish already.) In Spanish we use the singular to ask for the hour, "Qué hora es?" in Portuguese it is plural: Que horas são?
There is a difference as well in the time specification. In both languages the verb has to comply with the hours, which are feminine, in number. It it is only one hour the verb is é: É uma hora. If there are several hours, what it the case 23 hours a day, the verb is in plural, são: São três horas. However in opposite to Spanish there is no article. In Spanish it is "Es la una" and "Son las tres". There is an article in front of the hour.
The day has, nothing really new, 24 hours and for unknown reasons these 24 hours are splittet in two parts. From midnight to midday and from midday to midnight, each of these parts having 12 hours. Most of the watches on earth, at least the ones with pointers, have only 12 hours, therefore we have to know whether we are in the first or the second part of the day. (Actually there are watches with 24 hours, but these watches are actually confusing.) If there is a need to specify whether an appointement is at six o clock in the morning or at six o clock in the evening in English we can add a.m. or p.m. (a.m = ante meridiem, before midday <=> p.m. = post meridiem, after midday.)
In Portuguese and Spanish this distinction is made, if needed, with adverbs.
0 o' clock until 6 o'clock
= da madrugada (in the morning)
6 o' clock until 12 o'clock
= da manhã (in the morning)
12 o' clock until 18 o'clock
= da tarde (in the evening)
18 o' clock until 24 o'clock
= da noite (at night)
It can be questioned whether or not the madrugada ends exactly at six o' clock in the morning and the tarde exactly at 6 o' clock in the evening, but it is precise enough.
If special emphasis is wanted on the fact that a full hour is accomplished it is possible to add em ponto.
São cinco horas em ponto.
At five o' clock sharp.
One should see that in Portuguese not only one, um / uma / uns / umas has to comply in number and gender with the noun, but two, dois / duas as well and since hora is feminine, it is duas horas and not dois horas. In the table at the end of the page the part of the day, da madrugada, da manhã, da tarde, da noite is added, although this is not always necessary.
To the full hour the minutes are added or deducted. There is no rule establishing whether the minutes are added or subducted.
São cinco e quarenta.
It is fourty minutes past five.
São vinte para as seis.
It is twenty minutes to six. .
For midnight and midday there are special expressions.
É meio-dia. = It is midday.
É meia-note. It is midnight.
+ addition to full hour
time in digitals
optional: a.m / p.m
e quarenta e cinco
It is one hour and fourty-five in the morning
It is one hour and five in the afternoon
e quarenta e cinco
They are forteen hours and fourty five in the afternoon
e trinta e cinco
They are four hours and thirty-five minutes in the morning
It is one hour and twenty in the morning
It is three hours and fifteen in the morning
It is four hours an thirty in the afternoon
vinte e uma horas
It is twenty-on hours in in the evening
There are 10 hours and fourteen in the morning
e vinte e um
There are two hours
* If the time is told in military time, da madrugada, da tarde, da manhã, da noite is obviously useless. In this case it is clear to which part of the day the time specification belongs to. The specification is superfluous as well if everybody participating in the conversation know to which part of the day the time specification refers too. If some people make a date for dinner it superfluous to say that it is at oito horas da noite. We added it here for didactical reasons.
In Brasilian Portuguese missing minutes to the full hour are indicated with para. (Twenty minutes for four o' clock.) This changes as well the basic structure. Now the minutes are before the verb and an article is used.
minute missing to full hour
para + hour
time in digitals
optional a.m. / p.m.
vinte e cinco
para as três
Are twenty-five minutes for three
para as três
Are twenty minutes for three
para as seis
Are twenty minutes for six o' clock in the morning
In European Portuguese the minutes can be deducted as well, what corresponds to the Spanish solution. (Spanish: Son las seis menos veinte.) Furthermore it is not common in Brasil to construct with quarters. (a quarter to twelve.) In European Portuguese this is possible. If the minutes are deducted we have the same structure as if the were added.