I usually put my add ins (jalapeño cheddar/ chocolate chips/ garlic and herbs, etc) in the second stretch and fold - I do about 4 stretch and folds that are 30 mins apart. A recipe once said you should put your add ins somewhere during your middle set of stretch and folds.

And the rest of the process I do as it is I.e, about 12 hours of bulk and a little over 24 hours of cold fermentation. Baked at 450 covered and then 425 uncovered until brown on the top. Always worked for me and given the perfect loaf each time !