I've found that Freestyle L110 concentrate (HC110) doesn't last long once the bottle is opened. When freshly opened it's very good but after a month or so, unlike Kodakbrand, it oxidized and activity decreases quickly. This woul also explain why you have to expose at EI250 and still get thin shadows. Typically TMax 400 is a full box speed film unlike TX.
Under exposure or over exposure can increase apparent grain. Missed focus can make grain appear more noticeable. I found in the 60's that film is sensitive to heat and increased grain. I think it's less of a problem now due to improved emulsions but just varying rolls of TX in ones pocket for a while caused increased grain. After all your body is 98.6F which is pretty warm. Rapid and extreme changes in chemical temperatures can cause increased grain. In the 70's and earlier films were prone to reticulation but not any longer. I would however try to keep all chemicals and my wash within a couple of degrees. The best practice is to run B&W like you're running color. It may sound extreme but it's served me well for 5 decades and tens of thousands of rolls.
As to longer wet times, yes technically they can cause more grain. I read an article in the 60's that's still valid. Basically gelatin that is the binder for the silver halide on the film becomes soft and somewhat fluid when wet. It doesn't flow like water but it becomes very elastic and soft. Granted prehardening film during manufacture helps this but it's still soft and semi fluid. Anyway silver halide crystals are polar and tend to migrate or clump in this semi fluid environment. The crystals migrate from areas of less density to areas of more density especially when solvents like sodium Sulfite are present. So yes technically the longer in solution, the more opportunity for clumping and increasing of grain. In the 60's and 70's it was more of an issue but today it's less likely you'll see any effect. I still however like to use a hypo clearing bath for a couple of reasons. One it reduces water use, two it removes the last residual fixer and increases perminance, three with TMax it helps remove the antihalation dye and four it reduces wet time and potentially may reduce grain.
