There may be changes from day to day but, generally, parts of your behavior are habitual and time controlled. If you were honest with yourself, you'd realize that time-controlled behavior is fairly easy to start. And if the behavior is started at a habitual time, you will find that it is easier to get going without daydreaming or talking about other things. Don't start any unfinished business just before the time to start studying. Most people tend to think about jobs they haven't finished or obligations they have to fulfill much more than things that they have done and gotten out of the way.
Uncompleted activities tend to be remembered much longer than completed ones.
If we apply that idea to the habit of daydreaming, you might suspect that uncompleted activities and obligations would be more likely to crop up as a source of daydreaming than completed ones. Therefore, when you know you're about to start studying because it's the time you select to begin, don't get involved in long discussions. Try to be habitual with the time you start, and be careful what you do before you start studying. This can be one way to improve your ability to concentrate. Set small, short-range subgoals for yourself.