Expressing "constantly" with 时刻 and 时时
The adverb 时刻
时刻 
emphasizes that an action is performed continuously.
emphasizes that an action is performed continuously.Examples
司机在驾驶时必须时刻保持警惕
A driver must be alert at all times while driving
sījī zài jiàshǐ shí bìxū shíkè bǎochí jǐnɡtì
父母时刻关注着孩子的成长
Parents are always concerned about their child's development
fùmǔ shíkè ɡuānzhù zhe háizi de chénɡzhǎnɡ
时刻 can also mean "moment" and "in a moment".
Examples
我不会忘记这个幸福的时刻
I will never forget this happy moment
wǒ bú huì wàngjì zhè ge xìngfú de shíkè
他时刻都能来
He can come at any time
tā shíkè dōu néng lái
The adverb 时时
The adverb 时时 also emphasizes that an action is continuous.
also emphasizes that an action is continuous.Examples
市场时时都在变化
The market is always changing
shìchǎng shíshí dōu zài biànhuà
老师时时关注着我们的学习
The teacher always monitors our academic performance
lǎoshī shíshí guānzhùzhe wǒmen de xuéxí