You can begin pulling DMT within an hour or so. But to tell how long you should let it set to get the maximum yield, that Is a complex answer. There are many factors that need to be accounted for. The temperature of the room your using, the total volume of your extraction materials, the actual pH of your solution, and the efficacy of your solvent. From my experience, I like let my lye and root bark mixture set for an hour or so, with some shaking, then add your solvent. The first pull can be made within another hour and yield DMT, albeit a percentage of the overall, extractable DMT. My sweet spot is letting my lye solution and solvent set for around 6 hours per pull, with occasional shaking and rolling. While this works for my extraction set up, you might find that less or more time can be added to your set up, resulting in greater yields. As a rule of thumb, I would let the solution set for an hour after first mixing, then add your solvent and wait for
AT LEAST another hour before doing your first pull. You will find after 2-3 extractions using the same tek, what works best for the equipment and materials you have.
As a side note there are plenty of reports of people making succesful extractions by letting their materials set for days or weeks (mostly with large, several kg extractions) but this does not seem to effect their overall yield. You might get more plant fats and what not by letting it set for longer (which in my opinion isn't the biggest deal but that's just me), but the overall amount of DMT extracted will be greater.
You may think you can or think you can't; either way you're right.