If it's something like a day planner, and you're making a list of things that you'll do the next day, you can write, "wake up at 6am, go to work at 8am...."
If you're writing the diary at the end of the day, as a recording of the events of the day, you can write, "I woke up at 6am. I went to work at 8am...."
I usually write my diary in the 2nd way.