Hi Colin and Welcome to the forum, you might want to have a look at the following FAQ which explains where everything is
Welcome to Benefits and Work I have moved your query to its own topic to save confusion.
In reality, ESA is an open ended award that can be reassessed at any time once 3 months has passed since the decision. The length of award does not form part of the decision and cannot be appealed.
At the moment the system has a huge backlog, so you could well find that it is more than 12 months before you are reassessed anyway.
If you have further questions, please reply to this message and we will do our best to help