You are correct that as the water gets colder and the sun is lower in the sky, then the SWG on-time can generally get reduced and this will reduce the rate of pH rise (due to less chlorine and carbon dioxide outgassing). If your TA is high, however, the pH can rise even without an SWG. Lowering the TA level (to around 80 ppm) is one way to reduce the rate of pH rise in general.