Systems and methods for providing flexible time masks for transmission in a wireless communication system are disclosed. In some embodiments, a method of operation of a node in a wireless communication system comprises providing, to a wireless device, an indication of a position of a transient period during a time mask, where the position of the transient period is adapted to a clear channel assessment period at the wireless device or the position of the transient period is such that the transient period occurs at least partially during a clear channel assessment period. The time mask defines an OFF period during which a transmitter of the wireless device is to be off, an ON period during which the transmitter of the wireless device is to be on, and the transient period. The transient period is a period during which the transmitter of the wireless device is to ramp-up or ramp-down.