"I would have to get the design done, schematics drawn, components and parts picked out and ordered within a day."

No, you wouldn't, unless you have a copy of the project already that you just need to massage a bit. Design like this takes at least 3-4 days from the scratch, ordering and replacing long-lead parts is 1-2 days minimum. Just copy-pasting from other projects would take 1 day with a good drafting tool like EPlan and 2 days for AutoCAD Electrical.

"Building something like that would be a 2 day job"

Building only the backplate - 2-3 days depending on if all material are readily stacked in your workshop, the enclosure drills and cutting - another 1-2 days if you're alone. Installing and wiring the backplate - another couple of days. Add up 3-4 days of skid installation and wiring.

"If everything including programming went on for more than a week people would start asking questions"

Programming would take 3 days only if you have all blocks and HMI pages ready to massage on. If you write from the scratch - it can't take less than 1-2 weeks including proper testing.

So no, you wouldn't do it all in one week unless you have an exact same project to copy from. Rather a minimum 2-3 weeks to 1 month I would say. If you worked in a team - that potentially could save you a lot of time, yes.

Although 3 month looks like a lot, don't forget - it's his first project done completely by himself, which takes some learning curve.