Pedro, you could likely chime in on this, but from what I gather, for most families wash day was on Monday and lasted until Tuesday or even Wednesday.
I've been reading about this lately after taking another look at a second-hand pair of Sugar Cane jeans I got from Japan. The previous owner had obviously washed them in very hot water as the patch was pretty well fried, but also because the weft was so white and the denim/fades had a different look and feel to it, and there was little in the way of damage or blowouts aside from an unraveling hem.
Since then I've been washing with soap powder and hot water but also reading more about how laundry was done in the past.
Here are some descriptions from the 1930s, for example:
"On a Sunday evening, copper and dolly tubs might be filled with cold water in preparation for wash day. Clothes were sorted and segregated into woollens and cottons and colours and whites. As modern day biological detergents were not available in 1939, exceptionally dirty clothing like overalls would be left to soak overnight with soap flakes added. White shirts and blouses would stand overnight in cold water containing a "blue" whitener.
At the start of wash day the electric copper was turned on, or a coal fire was lit under the brick copper to ensure that the water in the tubs was hot enough. A dolly peg, (an item resembling a four or six-legged wooden stool, out of which a wooden "T" piece protruded), would be used to agitate the items that had been soaking overnight. Rotating the dolly peg in this way was a physically demanding and tiring affair.
The washing process itself involved lifting the items from the cold soak and wringing or mangling each item before transferring them, with more soap flakes, into the copper for boiling. Items that remained soiled, even after an overnight soak, were rubbed on a scrubbing board before being transferred to the copper. A clothes mangle, a hand operated machine consisting of two rotating rollers (which presented a quite serious potential hazard to anyone not paying attention), would be used to squeeze out all the excess water. Clothes would then be hung out to dry on a clothes line, or laid over a clothes-horse next to the kitchen or living room fire."
Would jeans like these have gone through the same process?