twt event length prblem of Online Power Profiler for Wi-Fi

As shown in the figure, is the tool "Online Power Profiler for Wi-Fi"

TWT event length includes: crystal ramp-up, initialization,  start radio, receive,  transmit, and enter sleep.

DTIM event length includes: crystal ramp-up, initialization,  start radio, receive, and enter sleep.

why DTIM does not have the step of transmit and what does the meaning of transmit stand for? 

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