Start block session for the night with a certain action instead of a specific time

A regular block session for the night depending on the time does not work for me.
I would appreciate to have it with more flexibility. Similar to the blocking in the morning which depends on my actual wake up time.

Thinking of a journaling entry in the evening. When this is logged in, the blocking starts and can only be switched off in the morning after the morning countdown.
Would love to have this intentional moment to close the apps down for the night.