In brief, I believe that shutting down the shop, without warning, a day before maintenance is worse for the playerbase as a whole than whatever additional damage the exploiters could do in those 24 hours.
The two cases that stand out are those who planned on transferring ships (either lose out on 2 weeks of progress on new ship or have to eat shop losses) and those selling market items whose value will predictably decrease after maintenance (e.g. Val weapons after the new collection folders launch).
I'm sure I'm missing something, but it's just hard to imagine what would have to be fixed for net welfare to improve by closing the shop 24 hours early (e.g., fixing duplication benefits a few lucky/wealthy ARKs while increasing costs for the rest). On the other hand, the benefits to Sega of closing shop early are easier to fathom - duping decreases demand for scratch tickets, as does the ability to sell unsellable items. Though if the rationale is really to save a few bucks from one more day of exploits it just doesn't seem worth the PR hassle... But I'm making a lot of assumptions here so there's plenty of ways this logic could be wrong and I hope it is!
TL:DR - My suggestion is to either give 24+ hours notice before closing the shop or wait until after maintenance and ship transfers have gone through.