You should aim to spend between 1 and 3 weeks preparing for your test. Ideally to be done around the same time as your job application/s.
The reason being as you are applying for a group of jobs together, its very probable that you will get asked to do online psychometric test also around the same time.
You would be notified in a call or an email that you have progressed to the next stage and that you have to finish a test or a group of test that the company sets online.
You will have a deadline set between 1 day to 5 days from when you receive the email to do those tests.
Given the above scenario, preparing once you get a test would be way too late. You don't need the stress hence you have to prepare early.
The aim for numerical testing is SPEED. Most numerical tests are timed, meaning you have a set time to finish all questions. Some are timed per question, some just have an overall countdown timer.
A few boutique hedgefunds are known to give extremely hard questions that cannot be done in the time given. It is up to you to decide when you have to skip otherwise you might be sacrificing 5 or 6 questions just to get 1 question right.
Make sure you stay calm at all times and keep your eye on the clock.
When there is 1.5 mins left its time to make a judgement call. If you still have a lot of questions to get through you might want to skim and guess as you have a 25% chance of getting any question right (assuming its a mmultiple choice of 4 answers). Do this only for a maximum of 1-3 questions as accuracy might also be marked.
TIP: get a calculator with 2 memories and preferably big buttons! Practice on it! You want to practice in such a way that you will only ever need the calculator.
The aim for verbal reasoning "True, False, Cannot say" questions is also SPEED, you will have to practise reading faster, over 60% of candidates never finish this test due to slow reading speeds.
There are also adaptive tests that some companies use, what this means is that the questions progressively get harder and harder as you get more and more right, the purpose is to see how high you can go and level out. These are seldom timed but will still be under 30mins long.