Specifying travel visa dates vs accommodation dates

Question

I am looking to apply for a tourist visa to Russia by myself with the aid of this websites information.

I wish only to go for approximately 12 days but I would like to be flexible so I wish to apply for dates that span for as much as 25 days.

I understand that when I can complete the invitation visa information and the subsequent online visa application form that I need to provide hotel/hostel names and locations as well as expected days of transit. Nothing as yet is booked of course as I'm waiting for the entire application to be successful and as I plan on going to a couple of other places beforehand and wish to remain flexible there also my actual entry date may vary by up to a week.

As per this websites tips for filling out the application I can choose a hotel from a list and say I'm staying there and later change my mind but my question is should I provide information showing me having accommodation booked for say a full 25 day period or just a 12 day period but still ask for a 25 day or so window?

thanks

Paul