I've seen player injuries that take ages to sort out, and then have much less stoppage time than that. The ref just picked a number out of a hat.
If I'm not mistaken, we finished just about the same time as the ManUre game and they had the 9 minute delay for Luke Shaw's broken leg. That game also had five substitutions. Total lack of consistency between different officials.
Kayal and Baldock both down for at least 2 mins each, so it was probably about right