I've said it before, but I love my turbo trainer!
It depends on your ability to push yourself. Some people I know just sit on them for an hour or two and pedal away. Others batter themselves with interval training using videos like sufferfest.
I have turbo'd without and with videos and an hour without using a video, while manageable is soul destroyingly boring. No amount of music or book reading improves the situation.
IMHO nothing will improve your cycling fitness quicker than turbo training. After a winter on the turbo my first few rides on the road feel too easy!
Don't forget to get the biggest most powerful fan you can buy to get the air moving. Have a look in the diy shops, they will be selling them off cheap at the end of what used to be called summer. I think this year I might buy a second fan, it definitely helps.