look at the loop() function in the example I provided...
void loop()
{
static uint32_t lastMillis = 0;
if (millis() - lastMillis > 1000UL) //<<<<<<<< updates once per second...
{
char message[64] = "";
sprintf(message, "Fan1 Speed:%4d RPM\t%4d Hz", uint32_t(floor(fan1->getSpeed() + 0.5)), uint32_t(floor(fan1->getHertz() + 0.5)));
Serial.println(message);
sprintf(message, "Fan2 Speed:%4d RPM\t%4d Hz", uint32_t(floor(fan2->getSpeed() + 0.5)), uint32_t(floor(fan2->getHertz() + 0.5)));
Serial.println(message);
lastMillis = millis();
}
}