Countdown timers (CDTs) for pedestrians and cars have been shown to produce various effects, including improved efficiency and decreased safety. This study aimed to explore adaptive behaviours of cyclists towards a CDT to green traffic light, conducted as a before-after study in real traffic. Cyclists adapted to the CDT by searching for and using the information that it provided, mainly in terms of speed adaptation and glance behaviour. Start-up delays were reduced but there is a concern that red light violations could increase. There might be undesirable effects on crucial information intake in cases where the CDT was used not as a complement but as a substitute for the traffic light. The results essentially indicate that cyclists use the information provided by the CDT for their own efficiency, rather than for rule-based safety.