他們在這個時候一定已經到家了。

They must have arrived home by this time.

Source: Tatoeba

Sentence Composition

1 他們 tāmen they; them
2 在 zài
  1. to exist; to be alive
  2. (of sb or sth) to be (located) at
  3. (used before a verb to indicate an action in progress)
3 這個 zhège
  1. (pronoun) this
  2. (adjective) this
4 時候 shíhou
  1. time
  2. length of time
  3. moment
  4. period
5 一定 yīdìng
  1. surely
  2. certainly
  3. necessarily
  4. fixed
  5. a certain (extent etc)
  6. given
  7. particular
  8. must
6 已經 yǐjīng already
7 到家 dàojiā
  1. perfect
  2. excellent
  3. brought to the utmost degree
=8 了 le
  1. (completed action marker)
  2. (modal particle indicating change of state, situation now)
  3. (modal particle intensifying preceding clause)
=8 了 liǎo
  1. to finish
  2. (used with 得 dé or 不 bù after a verb to express (im)possibility, as in 忘不了 wàngbuliǎo "cannot forget")
  3. (literary) (usually followed by a negative such as 無 wú or 不 bù) completely (not); entirely (not); (not) in the least
  4. to understand clearly (variant of 瞭 liǎo)
=8 了 liǎo
  1. (of eyes) bright
  2. clear-sighted
  3. to understand clearly
=8 了 liào unofficial variant of 瞭 liào