Depends who you ask, and when. UPS customer service 800 number told me one thing, internet told me another, sign next to the door said something else. Probably M-F, small window in the morning, small window in the late afternoon early evening, looks like they just slap another sticker over the sign when they don't want to be there. Might be there other times, too, though definitely not weekends. I'd suggest you call first, but you can't. Word of advice, don't bother going, they won't help you, anyway.
3pm to 7pm but get there early Monday thru friday
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