After setting the pin TRX_PIN_SLP_TR = HIGH, the radio transceiver delivers another 35 clock cycles on the pin TRX_PIN_CLKM before it reaches the SLEEP state. With the default configuration of 1 MHz, the state transition happens within 35 us (see also section CLKM Frequency Change).
After setting the pin TRX_PIN_SLP_TR = LOW, the radio transceiver needs typically 880 us (refer to AT86RF230 data sheet) for wakeup. If the MCU is active during this transition, the software may poll the sub register SR_TRX_STATUS until the state TRX_OFF is reached.