Between fifty and sixty hours a week is more the norm than exception, yes, because you're typically expected to spend around ten hours in your store a day, with typically two days off a week. There are a lot of variables though. If you're assigned a lower volume store, you might be able to get away with leaving early if you're the closing co or coming in a bit late if you're the opening co. This depends on your store manager though and how efficient your employees are. If your store is understaffed/employees are really dissatisfied with their jobs and don't work that hard during their shifts, you will sometimes need to finish the work that they didn't. Then there are your fellow co-managers. Depending on whether they're lazy or efficient, this could mean more or less work for you to finish before you leave for the day. Bad thing is, corporate is pushing the co's to do more and more in order to make up for the fact that some hourly employees aren't excelling at what they're doing and corporate wants to limit hours in stores to bolster the bottom line, so you'll find yourself on registers, helping in produce/grocery and other departments, in addition to your typical duties as a co. Depending on how much you are used to "fill the gaps", how many hours you work a week can vary.

Holiday weeks are typically sixty to seventy hours. Big sales event weeks (Super Bowl, Valentine's and Mother's Day, Back to School, Holiday Open House, etc...) are longer weeks too, although not as intense as Thanksgiving/Christmas week. 

If you live in a part of the country that gets snow or can potentially get snow, that can really push your hours up, too, because when the weather calls for a bad snowstorm or the possibility of freezing rain, look out.

Key Retailing checks and corporate visits can also lead you to working more hours during a given week.

Ultimately, it's hard to give an average, but one thing is for sure: you need to be okay with spending more time in a Kroger store than your home before you become a co.