I looked at this one more time and changed my mind a bit.
Now I think it will be some speculation with logs from framework, if we will have a lot of Messages, on which the expression would provide an invalid result, but it is OK for end application logic.
So, I'd revert it to the DEBUG, as it was before and add an important note to the RM. And further I'd ask people on forums to switch on DEBUG level on `DelayHandler` to see what is an issue with their expression.
WDYT?