First how is your current cycling shape? I.e. how many miles do you ride a week, how strong and fast of a rider are you, how fast do you expect to want to go, etc. Depending on all these factors will determine how much you can improve in a months times.

But regardless you are probably going to get the best you can by simply riding alot of miles at the pace you are thinking of at this point. Of course there are quite a few good training plans out there for someone who wants to do something simular to what you are thinking about!