I had a somewhat similar problem with my new, dumb coffee machine that doesn't have an auto-off. It just kept the heating unit on until the switch was physically turned off (different from your curling iron which defaults to off after power removed). In my case, I just said how long should the thing be on before it's too long, and then just turned it off. It results in a simple rule:
(there is a second rule to hide the fact that the coffee machine power usage goes to 0w while cycling the heater, see Better Dumb Coffee Pot - #19 by jlv for details).
By all this, I wonder if this suggestion is simpler: simply turn off the outlet after the maximum time (45 minutes?) it should be used. Then wait 1 minute and turn it back on. Don't complicate the rule with presense.
