I installed the update for the official iOS Twitter icon a couple of days ago and noticed that even though the update advertised a new icon, the icon didn't change when the update installed. Today I just looked at my phone and the new icon is there. Is there usually a delay between update installation and icon update? If so, how long is it supposed to be and why does it occur?
There shouldn't be any delay. It's likely it's just a bug - perhaps one of the graphics files in the app file didn't get swapped out. It happened with Reeder for iPhone recently. Or the release notes were in error (I note they don't seem to mention any icon update now).