How long the boot sequence is?

Hello,

I have a prototype PCB which has a MCU and DA14580.
The UART interface is shared between DA14580 and another device. The DA14580 power source can't be turned off by MCU. Currently, I don't want to communicate with DA14580 and try to wait until the boot code get to endless loop as described in AN-B-001 document.
However, the document just said that

"Steps 7 to 11 are executed a total of 5 times. If no successful communication has been established by then, the DA14580 boot code will end in an endless (while) loop with the Serial Wire interface (JTAG) activated"

没有多长时间的信息DA14580 will get to the while(1) loop.
How long should MCU wait until it can safely communicate with other device on that UART interface?

Thanks,