Making a crystal from borax requires you to cool down a mixture of borax and water. When cooling this down, the borax is able to become a crystal faster than the water becomes ice. After cooling down this mixture, the borax will become a crystal, and the water will be left over.

If you would like a crystal to form quickly, you will need a lower temperature. With a colder temperature, your mixture will get colder much faster, and your borax will become a crystal faster.

However, since there is some dust and other particles in your solution, the dust can get in the way of your crystal. It will stop the growth of a big crystal and make more smaller crystals. Because you have less time for the crystal to form, the borax will not be able to avoid the dust and other particles when forming a crystal. If you would like a big crystal, then you want to give it plenty of time to cool down, so a warmer temperature would work best.

In conclusion, a crystal will be formed faster at low temperatures. At higher temperatures, your crystal will form slower, but will have more time to look pretty. I hope this answers your question!