The truth has a shelf life. Tell it late and it tastes like betrayal.

The same information changes meaning depending on when it arrives. Said early, it is honesty. Said after the other person could have used it, it carries the extra fact that you knew and held it, and that second part is what people react to, often more than to the thing itself.

If something is sitting with you, work out the last moment it would still be useful to them and speak before that. When you have already missed it, say both parts: what happened, and that you should have told them sooner. Naming the delay yourself takes most of the sting out.