If the format stays the same as last year they actually get less than 30 seconds a question because the Trafford 11+ NVR is four 8 minute sections of 17 questions each. So, whilst the Nelson NFER practice tests aren't exactly the same in terms of number of questions and timing they are very close. To clarify, the test is run in sections with an official start and stop at the end of each section.
If you look at http://www.elevenplusexams.co.uk/11-plus-trafford.php
on this website there is a lot of useful information about the exam, including the nugget above.
The timing is very tight. From our experience this year I recommend emphasising over and over again how important it is not to dwell on a question that is not obvious, to mark it and then move on. If you can eliminate 2 out of the 5 answers then do so, so when you come back to the question in any time left at the end of the section you can make a more educated guess.