I was flying MXP-EWR last February and the inbound CO flight (our aircraft) was 6+ hours late. I didn't even call CO, just arrived at the airport well in advance of the newly-scheduled departure time. No crowds at check-in (just one other party) and I avoided 4+ hours of the 6+ hour delay. Never once was mentioned to me that I should have checked in at the regularly-scheduled time. Sometimes it is best to ask for forgiveness than permission (though I didn't ask for either in my case)