How long is a piece of string?
Sometimes, I could get raised blood sugars a couple of days before a cold.
Sometimes I could get raised blood sugars the day before a cold.
Sometimes I could get raised blood sugars on the day my nose starts running.
Sometimes I get raised blood sugars and never get a cold.
If I see my blood sugars rise any sooner than 2 days before a cold, I probably put it down to something else (e.g. stress) and my mind does not associate the rise with the cold.
As a pedantic engineer, these are not spikes - a spike goes up and comes down quickly. These are raised blood sugars (they go up and stay up) unless I give myself extra insulin.