They are most active at around 6 pm. The males are constantly patrolling up and down the stream, and are sometimes engaged in brief but vigorous territorial fights. Many of them, especially the older males, have damaged wings as a result of these fights.
The male featured in the footage below has a clipped right hindwing. Whether this has affected his flight performance is not apparent. What is obvious is that he can still guard his territory, capture and mate with a female and protect her from harassment by other males while she is ovipositing (laying eggs). I believe this male will have his next generation thriving in Bishan stream.
Most of this footage was taken at 120 fps and 240 fps. Only 3 seconds of it (01:12 to 01:15) was taken at normal speed (30 fps). Please choose 480p video quality to view.