Try reading the actual value of potentiometer in a loop. Something like this:
int potpin = 0;
int ledpin = 13;
int val;
int lastChange; // the time of changing pin state
void setup()
{
pinMode(ledpin, OUTPUT);
val = map(analogRead(potpin), 0, 1023, 500, 5); // actual value
}
void loop()
{
digitalWrite(ledpin, HIGH);
lastChange = millis(); // ledpin state changed NOW
while(lastChange + val <= millis()) // loop while there's time for it :)
{
val = map(analogRead(potpin), 0, 1023, 500, 5); // read the value every time
}
// the same here:
digitalWrite(ledpin, LOW);
lastChange = millis();
while(lastChange + val <= millis())
{
val = map(analogRead(potpin), 0, 1023, 500, 5);
}
}
I didn't check it, I don't have the access to IDE right now, but maybe it will work 