Same sentiment as pretty much everyone above - did you sign your name to anything when taking on the job that included a clause obliging you to give notice when leaving or face action? (You did READ the boilerplate, yeah?)
Or is this a strictly temp-casual kind of affair, like most high street retail jobs are, where if things are going well they'll be happy to keep you on for life, but if you suck - they suck - or the market sucks and there's no more money, you can walk (or be told to) at the end of the week / end of the day / end of this sentence?
I'm pretty sure there's even certain legal things involved in it depending on where you live. Here in the UK, if you've worked a "permanent" (ie indefinite, rolling or long-term contract) job for more than six months (or I think it's two years?) you HAVE to be given - and give - a certain amount of notice of termination ... so, having been mutually wrenched out of your happy little relationship, you can find a new job to replace your steady one, and your employer can at least start looking for someone else to take your place, and instigate damage control measures until they're in-post. Before that period has been worked, you have no enshrined rights - or obligations. It's all up to what you may have signed. A lot of employers make the first few weeks or months an explicit "probation" period where if they don't like you, or you don't like them, it's game over as soon as you like. (And in my immediate predecessor's case, they offer the job to the second place interviewee... namely moi, who leaps at it on the offchance it was "wrong employee" not "wrong job" and isn't disappointed).
I've been there, I'm sure we all have. Some jobs and/or some bosses just suck choad. It can even be that the job is excellent but the people suck, and vice versa (I've had both) and all you can do is cut your losses and GTFO. It's hard on the other people you leave behind who have to cover for you, but in such environments, you have to look after yourself first of all. Once you find somewhere that it all actually clicks, you'll forget it and instead laugh at them for sticking it out so long.
I would be willing to bet that he hasn't got a legal leg to stand on here, either contractural or regulatory, and he's just apprehensive of having all manner of problems in the shop over the next -however long- until a suitable replacement buttmonkey can be conned into the job. Two weeks should be long enough to advertise for, briefly interview and hire someone to cover you, but 24 hours isn't.
Tell him to shove it and go find somewhere and someone better. Send a long voicemail consisting of David Allen Coe's "Take This Job..." and A's "Starbucks" on repeat. And if all else fails, give your notice and just call in sick for two straight weeks. By the time you're called upon to self certify or provide a doctor's note, you're out of there.