The Adverb 才(cái)
The adverb 才 indicates that the occurrence of an action or situation is later than the speaker may have expected. That lateness is perceived by the speaker, and is not necessarily objective. 才 never takes the particle ,了 whether or not it pertains to an action or situation in the past.
Ex) 他晚上很晚才睡觉。
Ex) 他晚上很晚才睡觉。