adirao -- If your oven takes longer, there's a good chance that the temperature inside is lower than it says on your dial or display.
Go buy an oven thermometer -- it's like $5, and it will help ensure that you heat your oven to the correct temperature.
For example, when I bought one I discovered that my oven ran about 15 degrees (F) too cool. Even when I made the proper adjustments (the owner's manual detailed a way to adjust the digital temp display), it still took another 5-10 minutes after the "I'm ready" beep for the temperature to actually reach the real temperature I wanted.
But at the very least, get yourself that thermometer! :)