Every Friday morning...out of the house by 8 a.m., Saturday by 9 a.m. if we didn't go on Friday, and sometimes Sunday mornings, depending on the weather and our moods. I think estate sales will produce fabric and machines more so than garage/yard sales, just my opinion and experience. I have nearly built an entire stash on garage and estate sales and remnants! FUN!
We try to pick a different part of town each week, and he first weekend of the month is usually the best time to go, since many people wait til then to have their sales figuring on everyone getting paid on the first of the month. You can often get better deals late in the day on Saturday or Sunday as the sellers are closing down and don't want to have to find a place to put the leftovers...assuming there's anything left worth buying.
I haven't figured out the thrift store times and days yet but have a neighbor who finds some great fabric deals. I need to start figuring that out soon, since there aren't many garage sales through the winter months.