‘sa3a’ means both ‘hour’ and ‘watch, clock’.

Use the feminine cardinal numbers:

is-sa3a thintayn – It’s two o’clock.
is-sa3a sitta – It’s six o’clock.
is-sa3a thimaanya – It’s eight o’clock.

x wa rub3 – a quarter past x. (lit. and a quarter)
x wa thilth – twenty past x. (lit. and a third.)
x wa nuSS – half past x. (lit. and a half.)

x illa rub3 – a quarter to x. (lit. but a quarter)
x illa thilth – twenty to x. (lit. but a third.)

is-sa3a ithna3ashr wa thilth – it’s 12:20.
is-sa3a thalaatha wa nuSS – It’s 3:30.
is-sa3a 3ashra illa rub3 – It’s 9:45.

dagiiga, pl. digaayig – minute
“dagiiga/digaayig’ is usually not used when telling the time, but it affects the gender you use when you say ‘five past/to’ and ‘ten past/to’. Use the masculine:

is-sa3a arba3a wa xams – It’s 4:05.
is-sa3a waa7da illa 3ashar – It’s 12:50.

To be more specific in Arabic language, you can add one of the following time expressions:

iS-Sub7 – in the morning
ba3ad iDH-Dhuhur – in the afternoon
il-3aSir – late afternoon (4-6 o’clock)
il-layl – at night (‘layl’ is anytime when it’s dark outside)