I'll start off with a very important warning for us English speakers: Frisian follows the same pattern as Dutch for the half-hour. It looks ahead to the hour that is coming up, not back to the hour past like we do in English!
E.g., our "half past four" is literally a half until five!
Hoe let is it?
Literally: How late is it; what time is it?
[HOO LEHt IHs UHT?]
It is twa oere. It is sân oere.
It is two o'clock. It is seven o'clock
[UHT IHs TWAH OOr-ruh. UHT IHs SAWn OOr-ruh]
Use normal numbers for telling the hour. This changes when we look at half-hours:
Literally: halfway to five; half past four (4:30).
You can say: healwei ienen (12:30), healwei twaen (1:30), healwei trijen (2:30), healwei fjouweren (3:30)... healwei seizen (5:30), healwei sânen (6:30), healwei achten (7:30), healwei njoggenen (8:30), healwei tsienen (9:30), healwei alven (10:30), and healwei tolven (11:30).
Notably, the twenty-four hour clock ("military time") is also used.
If we want to say that it is fifteen past an hour, we use the preposition oer, pronounced with a long "oo" sound. [OOr].
Kertier oer achten.
Literally: a quarter over eight; eight fifteen, 8:15
[keh-TEER OOr AHkh-tuhn]
However, another way to say fifteen past is to say the hour, oere, and then fifteen. It is confusing, yes. The hour name comes before in this case. Listen for that critical extra schwa that distinguishes the word for "hour," oere [OOr-ruh], from the word for "over," oer [OOr].
Sechtjin oere fyftjin
16:15... 4:15 P.M.
[SEHkh-tyuhn OOr-ruh FIHf-tyuhn]
Santjin oere fyftjin
17:15... 5:15 P.M.
[SAWn-tyuhn OOr-ruh FIHf-tyuhn]
Anyways, back to quarters. Conveniently, the Frisian word kertier looks a bit like the English word "quarter." Stress is on the second syllable, which is said with a long "ee" like in "tear," which we are all probably shedding by now as we try to tell time in Frisian. The first syllable takes a short "ih" like in "kit."
As we were saying, a "quarter past" is kertier oer. To say it is a quarter before, we use the preposition foar:
Kertier foar fjouweren. Kertier foar achten.
Quarter to four. Quarter to eight.
[kih-TEER FWAWr FYOW-wuh-ruhn]
[kih-TEER FWAWr AHkh-tuhn]
Similarly, if we want to say "twenty before," it's tweintich foar:
Tweintich foar fiven.
Twenty before five.
[TVIGHn-tukh FWAWr FEE-vuhn]
Twenty after five is: Tweintich oer fiven.
Finally, telling time with "twenty five" before or after can get really obnoxious. The half-hour is used like an anchor, which you'll remember looks forward to the next hour unlike in English.
So, twenty five to seven--or 6:35 to the English eye--is literally said "five over the half to seven."
Fiif oer hielwei sânen.
[FEEf OOr EEL-vigh SAHn-nuhn]
I wouldn't recommend sweating about this too much. Just be aware that it's something you might see. The basics of healwei, kertier, oer, and foar should take you very far.