I agree that the time taken to lay an egg can not only vary between the individual chickens but have also found that depending on the size of the egg or when she last laid, an individual chicken can sometimes be quick about it or make a meal of it.
I have found that with my gals, it can depend on circumstances also … if they are out free ranging they might just dash back to the nest box, get the deed done and off out again whereas if they are in the coop and run and not free ranging, they linger a little.