Welcome to Coffee Snobs Bickys.
If you do a search you will find lots of answers to your question.
Dont forget to change the default setting to more than one week.
In a nutshell though, unless youre an electronics genius (Im not) the heating element is linked to the fan and lowering the temperature usually also slows the fan which leads to other problems.
And yes, if you can lengthen the roast time youll get a better roast.
Its all been done before; which popper do you have?