I have the above visa (date of application 10th October 2016) I arrive in Australia on 1st March 2017. I leave Australia on 12th April 2017. My visit is help my daughter with her wedding preparation on 8th April. She has now asked that I come earlier. If I can find an earlier flight where do I stand with this visa - do I have to change it and if so how? Many thanks in anticipation.
The eVisitor visa is valid from the date it is granted for twelve months, and you can't stay for longer than three months during a visit:
You can stay in Australia for up to three months on each visit within 12 months from the date your eVisitor is granted. (source)
So if you have a eVisitor that was granted in October, you are okay to change your travel dates as long as you're not going to stay longer than three months.