As I stated in an earlier post in this thread, I generally keep my soldering iron at 300°C when soldering, but that doesn't mean that the part ever gets to that temperature. It takes time for heat to conduct from the tip through the solder, into the lead and on into the component. When the data sheet specified a maximum temperature and time (e.g. 250°C for 10 seconds) it is generally regarding a reflow profile. In other words, it assumes the component is in an oven bringing the entire assembly to that temperature. As an exercise, next time you are soldering a component onto a board, put a thermocouple on the part and monitor the temperature of the part body. you know when the solder melts that it's (probably) about 185°C. And since you take away the iron once the solder melts (or pretty quickly thereafter) it's unlikely that the body will ever get that hot. For the record, the reason I use a slightly higher iron temperature when soldering is so that the iron will be able to melt the solder quickly and without taking so much time as to allow the heat to flow very far past the leads.