Işe saat dokuze yermi kala çıkacağim. I am leaving for work at 7.40.

thank you

" İşe saat dokuza yirmi kala çıkacağım = I am leaving for work at 8.40

 "İşe saat sekize yirmi kala çıkacağım =  I am leaving for work at 7.40

"Işe saat dokuze yermi kala çıkacağim. I am leaving for work at 7.40."

İşe saat sekize yirmi kala gideceğim. or

İşe gitmek için saat sekize yirmi kala evden çıkacağım. (işe gitmek için = in order to go to work) ev=home evden=from home

if we rewrite these sentences for present then;

gideceğim----> giderim/gidiyorum, çıkacağım----> çıkarım/çıkıyorum

If you use the future tense here, it means you will do this one time. but if you use the present or continues, we understand that you always go to work at this hour.

could you explain the kala çıkıyorum part please

 It is an idiom. "Sekize yirmi kala çıkıyorum" meaning is "i´m leaving/departing twenty to eight."

The ´kala´ part is from the word used to say ´at´ when saying the time is at xxx to yyy (I guess from kalmak, to remain, to stay.

Here is a short piece about saying ´at´ a certain time.

To say ´at´ a certain time such as ´at half 8´, these are the formulas.

The formula for ´at...past...´ is;

hour + -(y)i + minute +geçe

examples
altı on geçe = at 10 past 6
ikiyi çeyrek geçe = at quarter past 2

The formula for ´at....to...´ is;

hour +-(y)a/e +minute + kala

examples
dokuza beş kala = at 5 to 9
sekize çeyrek kala = at quarter to 8

at 8 o´clock = (saat) sekizde
at half past 4 = (saat) dört buçukta

 Doesnt have to be "işten çıkacağım ?

 İşten çıkacağım is I will leave work

 Aha ok.

"kala"s equivelant in English can be "to" but not "at". "at"s equivalent is "-de,-da"

Sekize on kala işe gideceğim.

I will go to work at ten to eight.

There is no equivalent of "at" in the Turkish sentence. Because there is no need to use it.

Sekizde işe gideceğim.

I will go to work at eight.

As you can see in the Turkish sentence there is "-de" which is the equivalent of "at" Because it is necessary to use it.