i dont get it isnt millis() function just to keep track of time since the program started
I know you have looked at an alternate solution but:-
If you know how long the Arduino has been running (and you don't actually want to know that directly). Then that time plus 500 will be how long the Arduino has been running when you want to end your delay.
In this way you can do the equivalent to delay(500) but still able to do stuff during it. 
A potentiometer with three wires. Outside to +5v, other side to ground centre to analogue in. It doesn't matter which side is +5v