No flowchart required -
unsigned long currentMillis = millis();
if(currentMillis - previousMillis > interval) {
// save the last time you blinked the LED
previousMillis = currentMillis;
// if the LED is off turn it on and vice-versa:
if (ledState == LOW) {
ledState = HIGH;
interval = ON_TIME;
}
else
{
ledState = LOW;
interval = OFF_TIME;
}