Timing mental arithmetic training for specific event A test will take place in two months time. It will take place on 12:00 PM, and the test takes one hour. One has to perform tasks such as a basic IQ test, mental arithmetic and solving a sudoku. These types of tasks are known in advance.

Someone wants to train for this event by performing the tasks on a regular basis. What would be a good training schedule? Would it be best to train every day for an hour at exactly 12:00 PM, to condition the brain, or would it be better to train at random times to improve the brain's flexibility? Also, would it be better to take days off to have the brain rest, like you would do when training your body?
Firstly, I think you’re thinking too much tbh. But still, I would totally answer this question- I think both are good approaches. But at different period of time. Suppose it’s after a month. So for the first 20 days you work on different time period. It’s better you work longer- what I mean is you start by giving one sample test in one hour then take a 15 minutes break. Then again you do it for 3-4 hours. Take a good nap for 1-2 hours. Then again do it. 
In the last 10 days. You practise hard at 12PM  for sure. But you also practise in the remaining time. Because you need the brain to work. Simple example- if a car is switched off for 30 days it will take time to start. But if it switched off 39 minutes back it will start asap. Think about it. 

I hope it helps.