Depends on the company. Some explicitly say 60 days from purchase date, which is the date the order was made. Some say 60 days within receipt.
Yes, each company is different. With most things being logged on computers nowadays,
some companies can track and adjust the return date according to when items arrive. Other companies which don't have that kind of advanced software, I think, just use the order date OR the ship date.
I tend to return things by the order date. This way, it doesn't matter if they had given me an extension to ship date or arrival date. I'm safe.
For the OP, she would have had to return items by Sept 14.
(Some months have 30 day and others 31, so that may throw off one off adding up the days in your head. Meanwhile, the retailers' computers will be accurate. For instance, if the OP returned her items on Sept 17, it would have been the 62 day mark. She was over by an extra two days as July & Aug have 31 days.
)
If anyone needs an online calculator to figure out how many days something is, here is a good one. Make sure you checkmark, "Include end date in calculation (1 day is added)," as the day you return something will count as a day, not just the days in between.
https://www.timeanddate.com/date/duration.html