In my experience, it takes time and repetition to get into DBT skills. It takes understanding and effort of the skills, in order to really apply them to your life experiences. Writing in the daily DBT diary was a struggle for me as well, all throughout my group DBT meetings. I was inconsistent.

Don't bother making stuff up though: be honest! It only takes a few minutes per day of looking back, to answer which DBT skills that was used. Make a check-mark & write a clue to remind yourself how it was used, for later.

I really did enjoy group DBT, but yes, it takes some commitment to actually make a positive difference in your life.