One idea would be to open a Google doc or something and write out your thoughts and feelings late at night in a letter to your therapist. Even though you can't talk to her/him, you can still express the thoughts. What are you feeling? What triggered you? Why do you want to cut? What kind of relief do you want? What will you feel after you cut? What are some of the other things you've tried? What are some things you plan to do with the rest of your night?

By writing things down it helps us process things. And, seeing it written out can sometimes be cathartic. If you want you can choose to share it later with your therapist in session. It can be a good way to practice distraction and distress tolerance.

You can also take steps to make sure you're not so alone at night with your thoughts and demons. Either by connecting online, engaging in games, or even trying to go somewhere like the grocery store, a restaurant, or just outside.

These are things that were helpful for me in my recovery. Good luck and best wishes.