What is the ruling on a congregant delaying his tasleem until some time after the imam's tasleem?

The prescribed act for a congregant's salutation (taslim) is to say it immediately after the Imam's salutation, without delay, based on the Prophet's (peace be upon him) saying: "Indeed, the Imam is appointed to be followed, so do not differ from him." However, if the congregant's salutation is delayed after the Imam's, their prayer does not become invalid, because the following (iqtida') ceases with the Imam's salutation, and the congregant may delay as long as they wish.