The electric oven I have, Its maximum heat is only 250 Celsius. If I wanted to make a bun in it, 
How to preheat?
 & 
How much time I have to heat? 
&
how many Celsius to heat? 

[![enter image description here](https://i.stack.imgur.com/PysgS.jpg)](https://i.stack.imgur.com/PysgS.jpg)