Not wanting to ask a stupid question, but I downloaded 2 lots of practice dots tests. One of them said 30 seconds, the other said a minute! Obviously I got twice as far in a minute, but how long do you actually get in the real tests?
2 mins.
Way i practiced was with the same sheet 4 times. I photocopied them out of the "how to become a train driver" books.
I turned each one 90 degrees, so essentially i had 4 different sheets.
I then set up the stopwatch on my phone.
I then hammered all 4 sheets, pressing the "lap" every time i got to the end of the sheet.
To mark them then was easy as you just returned them all the right way up and analysed any differences between the sheets.
My "laptimes" ie time per sheet, and overall times, as well as mistakes made could then be compared.
I did this literally hundreds of times.
Did i improve?
There was a 1-2% improvement in time from first time to last as my eyes got more used to the shapes.
My laptimes remained constant as i was able to remain in a state of concentration.
What was noticeable was the increase in mistakes if i was distracted - if the cat jumped on the desk or i had a swig of tea or something.
Conclusion - practice has limited value. If you can't concentrate then you will make mistakes and won't pass. Simple.