It's common with any visa application to use estimated dates, since, in many cases, you wouldn't dare to book the flight until you know you have the visa approved.
If you haven't already done so, signup for the visa application portal and get the process going. I had mine sitting there half-finished for a couple of weeks.
If you have any specific questions, then fire away, but the process is pretty straightforward.
They ask you about your travel plans, but don't require any evidence.
It is speculated that they ask about your travel plans, in order to potentially prioritise applications. I don't think anyone actually knows this for sure though.