How to make Nlog with multiple target files with the same cached date-time in the file name

I am using Nlog 2.0 and I have 2 target files, one for our regular trace log and another for the error log. I use fileName="Error_${cached:cached=true:inner=${date:format=yyyyMMdd_HHmmss}}.txt"to give a consistent log file name for a single application run.

The problem is that the error log has a different time in the file name than the trace log because the error started to be logged much later. Right now, I resorted to sending an empty line at the beginning of the application to make both logs the same name. Is there a clear approach to this, i.e. One cached datetime for both purposes?