DS18S20 and all other OneWire bus devices cannot interrupt, its a strictly polling only bus.
If you do manage to attach an interrupt to the one-wire bus you'll get vast swaves of interrupts everytime you talk to the bus.
You need to regularly poll the DS18S20. You don't want to call delay(). So what you do is every second or so read the temperature from the device and set another conversion going. By the time the next second comes along the next conversion is guaranteed ready.
For doing some action on a regular basis with using delay please look at the BlinkWithoutDelay() example sketch...