Sigfox frame duration vary depending on the payload length. Optimizing the payload will result in valuable improvement of battery life and will increase the probability of receiving the frame.
Using ETSI (CE) modulation frame duration is as follow:
1 bit -> 1.12s
1 byte -> 1.2s
2-4 bytes -> 1.44s
5-8 bytes -> 1.76s
9-12 bytes -> 2.08s
Please note that this values are for a single Sigfox frame. A complete Sigfox frame being made of one frame repeated twice this value should be multiplied by 3 to get the real-life duration.