One way to ask the question "What is the time?" is ma tcika ti. We know that ma is the sumti question word ('what'), so tcika must be a selbri meaning 'is the time'. The place structure of tcika is
So in Lojban, times do not exist in the abstract: times are always the times of something. So we ask what the time is of ti, meaning 'this event/thing', or, in other words 'now'.x_{1} (hours, minutes, seconds) is the time of state/event x_{2} on day/date x_{3}, at location x_{4}, by calendar x_{5}
Note: Well, we don't really; stay tuned for next lesson, where we'll fill this in a little more.
A full answer would obviously be very longwinded, but remembering the Lojban convention that you miss out all the places after the last one you really need, a typical exchange would be:
Note the li, since we are talking about a number here. li papa is short for li papa cu tcika ti — "the number eleven is the time of this (event)".
ma tcika ti
li papa
What's the time?
Eleven
If we want to be a bit more precise, we need to use pi'e. This introduces fractional parts of numbers like pi, but unlike pi it doesn't need to indicate decimal fractions in a number. In fact, the kind of fractional part it does indicate can vary within the same number. In normal counting, pi is a decimal point, in hexadecimal it's a hexadecimal point and so on, but the kind of fraction it indicates never changes its value. But pi'e doesn't have that restriction; so we can use it to separate hours from minutes (which are sixtieths of hours), or, as we will see below, days from hours (which are twentyfourths of days). pi'e, in other words, means 'part', not 'decimal point'. So an alternative answer to the question could be
or if you want to be particularly precise,li papa pi'e mu
11:05 (Five past eleven)
(The number eleven, and five parts)
li papa pi'e mu pi'e pabi
Five minutes and eighteen seconds past eleven
(The number eleven, and five parts, and eighteen parts of parts)
Let's imagine, though, that the time is not five past eleven, but five to eleven. We can say li pano pi'e mumu (10:55), but we can also say li papa pi'e ni'u mu, where ni'u is the Lojban minus sign (for negative numbers, not for subtraction) — what we are saying is '11:−5'.
For 'half past eleven' you can also use pi and say li papa pimu '11.5'. I don't particularly like this method, but it is perfectly good Lojban. If we are using numbers for times, it is normal to use the 24hour system, so 6 PM is li pabi (18:00).
If you want to use twelvehour time instead, you need some way of distinguishing between AM and PM. The conventional way in Lojban is to use cmene for hours (so we can add supplementary information like that later on, as part of the cmene.) So 'four o'clock' is la vocac., 'five o'clock' is la mucac. and so on (from cacra 'hour'). For 11 and 12 we need extra numbers. Fortunately Lojban has these and more; the number system actually goes up to 16 (hexadecimal), so we have the extra numbers
dau  10  
fei  11  
gai  12  
jau  13  
rei  14  
vai  15 
As you can see, things start to get a little messy with the 12hour system (how do you say 9:22 AM?), so the 24hour system is preferred by popular acclamation.
Exercise 1 
What are the following times in Lojban?
