Our ability to process numerical and temporal information is an evolutionary skill thought to originate from a common magnitude system. In line with a common magnitude system, we have previously shown that adaptation to duration alters numerosity perception. Here, we investigate two hypotheses on how duration influences numerosity perception. A channel-based hypothesis predicts that numerosity perception is influenced by adaptation of onset/offset duration channels which also encode numerosity or wire together with numerosity channels (duration/numerosity channels). Hence, the onset/offset duration of the adapter is driving the effect regardless of the total duration of adaptation. A strength-of-adaptation hypothesis predicts that the effect of duration on numerosity perception is driven by the adaptation of numerosity channels only, with the total duration of adaptation driving the effect regardless of the onset/offset duration of the adapter. We performed two experiments where we manipulated the onset/offset duration of the adapter, the adapter's total presentation time, and the total duration of the adaptation trial. The first experiment tested the effect of adaptation to duration on numerosity discrimination, whereas the second experiment tested the effect of adaptation to numerosity and duration on numerosity discrimination. We found that the effect of adaptation to duration on numerosity perception is primarily driven by adapting duration/numerosity channels, supporting the channel-based hypothesis. In contrast, the effect of adaptation to numerosity on numerosity perception appears to be driven by the total duration of the adaptation trial, supporting the strength-of-adaptation hypothesis. Thus, we show that adaptation of at least two temporal mechanisms influences numerosity perception.