Is it okay to apply for a job on the weekend? retail and restaurants type jobs...best time?

also if you applied for a job online and there's a automatic msg that says it will contact you in 15 days if your qualified is it alright if I call up to follow up after a few days or should I just wait?
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I would check back on earlier in the week like Money or Tuesday when most places aren't really busy.
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It is okay to call back, but pretty much all the hiring managers work normal business hours(M-F 9-5).