interesting that LENR deniers can quote such a fact without asking the question why a pure Ohmic heater of < 500 grams needs 17 minutes for reaching a steady state...
The thermal gradient to the inside is much, much less than the thermal gradient to the outside. So most of the heat goes to the outside, leaving little to heat the core. At steady state the core temperature is actually similar to the coil temperature (how could it be any higher by conduction?). The core is 10 mm from the heater coil, while the outside is 2.5 mm away and has a very large favourable thermal gradient, with an “infinite” ambient (low temperature) reservoir to fill, aided by convection and radiation which is much more effective than conduction heat transfer.
Feel free to calculate what percentage of heat flows outward from the coil compared to flowing inward, as a function of time starting from a substantial coil temperature increase.
Placing the cylinder into a highly insulated cavity will greatly increase the rate at which the steady state condition is reached, by strongly limiting heat transfer outward, so more heat is available to heat the core.
One could similarly ask why it takes the outside only about 11 minutes to cool from 750 C to 200 C, but over an hour to cool from 200 C to 20 C.