In wiring.c delayMicroseconds() function using SBIW and BNRE instructions for timing.
In AVR MCUs it takes usually 4 clock cycles while in LGT MCUs takes usually 3 clock cycles.
Therefore this function delay less than expected.
I found a better version in a chinese site. The author corrected only 16 and 32 MHz cases.
https://www.geek-workshop.com/thread-38486-1-1.html