If someone already said this I'm sorry, I don't mean to be an

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You can leave PBW in contact with stainless steel for about 24hrs before it starts pitting the stainless. I also must advise not using HD orange buckets for any cleaning, sanitizing liquids or wort/beer. Those buckets are not food safe. Put in an extra $2 bucks and get a food safe bucket.
Personally I keep PBW in a 7 gallon wine bucket. You can keep it for a couple of days, but it works best for the first 24hrs.