it is not.
You can see the post ids in post.custom_fields['import_id']. But that’s just a counter of how many posts (or topics?) have been converted.
I’m pretty sure that the post has zero or null in some date field. it’s a warning, not an error, so it did import something. If it had failed to import it, you’d get an error, I’m fairly certain.
If you really care, you can modify the script to print the phpBB ID when it gets such an error, then you can track down which phpBB posts are generating these errors and look at those records to see what’s happening.
That date is zero in utime, so it wouldn’t change anything.
I’ve never thought it was worth my clients’ money to answer this question before. If it is something you’d like to spend money on, please email me.
Perhaps someone else has a better answer.