This is a genuine Casio F-91W with a custom negative/colour inverted display style. I think this configuration really suits the watch, and it's a shame Casio don't make them like this.
These are made to order, so dispatch time is up to 5 working days, but it is likely to be less.
Secondly, please be aware, this is a genuine watch. I have traded and collected Casio watches for many years, and out of curiosity purchased a ~£5 'genuine' stock F-91W on eBay, and it was most certainly not genuine. As a rule of thumb, I'd be wary of any standard watches costing less than £12, the price Casio and high street retailers charge.
These watches are sent in their original packaging. Being Casio's most cost effective (and thus most iconic) watch, the box doesn't offer much protection, unlike that of models slightly higher up the range. Accordingly, these sometimes annoyingly arrive with fine scuffs to the display, but for the most part, are absolutely fine. Despite what marketing may tell you, these resin displays do pick up scratches quite easily so if you wear it as often as you should, this won't be of concern.
I am a massive Casio fan so if you have any questions, please let me know.
Thanks.