To grow big crystals, there are mainly two ways. One is to evap the solvent VERY slowly. Cover the container only leaving tiny bit of space for air exchange, put in a quiet place with little air movement, and forget about it for many days. The very slow evaporation will facilitate very large crystals to form.
The other option is to freeze precipitate and alternating between higher and lower temperatures. So when one has the dmt-saturated naphtha, alternate a few times between fridge and room temperrature every couple of hours, then do the same but between fridge and freezer , and keep doing this for a few days. The idea is that the crystals start forming, and then when you move to higher temperature, the smaller crystals redissolve faster, and when you put in a colder place again the crystals tend to grow on top of the bigger ones that didnt redissolve.
there are a few other details like crystal seeding, or using an irregular surface object to help grow crystals (like a string hanging inside the freeze precip container), but basically the two ways I mentioned before are the main ideas behind it.