к шести часам

by six o’clock

→ к
phrase Rare #43,756
by six o’clock Indicates that something will happen no later than around 6:00. The preposition «к» takes the dative case here.
RU: Я постараюсь закончить работу к шести часам.
EN: I’ll try to finish the work by six o’clock.

Я ожидаю её возвращение к шести часам.

I expect her to return by six o’clock.

Будем на месте примерно к шести часам.

We'll be there by about six o'clock.

— Подводная лодка (1981)

Я вернусь к шести часам.

I'll be back by six o'clock.