An ‘incense stick of time’ is a phrase used in Xianxi books, which is a Chinese fantasy genre.
Definition: A poetic way of of referring to the amount of time it takes to burn an incense stick.
In these books, an ‘incense stick of time’ can be anywhere from 5 minutes to an hour.
However, it’s worth noting that most incense sticks today will burn for at least 30 to 45 minutes.
In ancient times, some people in Asia used incense sticks as a form of primitive clock, which is most likely where this phrase originally comes from.