Your finish time will depend on dozens of different factors, so it is very hard to predict. A training plan is just one part of the equation. The biggest determinant is your starting fitness and ability.
Improvements in run fitness happen gradually over a long period of time, if you train and recover effectively. There are no shortcuts unfortunately, even if you trained to the absolute best of your ability it might take you four or five years to reach your full potential.
First and foremost you need to pace it right based on your race day fitness, rather than what you hope to achieve. If you chase a time, you will probably race too hard and then suffer later.
If it is your first experience at the distance it's better not to set too many expectations. Just use the race to build experience.
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