The technical reason is discovery time
Real detailing uncovers things. A wash exposes a chip in the leading edge paint. A decontamination finds corrosion blooming at a fastener line. Cabin work turns up a failed seal, or a stain that needs a second treatment and a proper dry. FAA AC 43-4B puts corrosion inspection and treatment squarely on the operator, the manufacturer's recommendations or the operator's own program, and washing matters because it removes the acidic airborne contaminants that drive filiform corrosion under paint. With a week in hand those findings become managed items: photographed, reported, treated or scheduled. With twelve hours in hand they are either ignored or rushed.
Chemistry needs conditions, not goodwill
Coatings need controlled conditions and dwell time to cure. A coating applied into a hangar that opens at dawn for a departure has had neither, and the film you end up with is not the film the product is capable of. Interiors run on the same clock. Carpet has to dry fully and you cannot force it, because heat-drying carpet above 100°F shrinks it, which is why operator guidance warns against exactly that. An aircraft that departs with damp carpet arrives smelling of damp carpet, which is the one outcome the cabin work was meant to prevent.
A detail and a reset are two different jobs
Gulfstream's own Completion Center Maintenance Handbook gives Chapter 12, task 12-26-00, to cleaning, with separate procedures for wood, granite, Lexan, vinyl laminate, plating, stainless steel, leather, vinyl, Aermat rubber, carpet and fabric. Eleven materials, eleven methods, and the cautions are specific: silicone polishes leave an oily residue on the urethane wood finish that can prevent a later repair, the urethane is non-absorbent so it must be cleaned before every third polish to stop build-up, and two fabrics of the same fibre content can behave differently, so you test on an inconspicuous area first. You cannot sequence eleven material procedures, plus correction and brightwork, into a night. A reset is a different product, not a shorter version of the same one.
The failure mode of choosing wrong
Rushed work is not less work. It is the same work twice. A coating that did not cure has to come off and go back on. A stain given one pass at midnight sets and then needs a specialist. Brightwork is the unforgiving case: Alclad is a thin pure-aluminium cladding, roughly two to five per cent of total sheet thickness, and going through it exposes the copper-bearing 2024-T3 underneath to air and water. Paint correction has the same one-way character. The clearcoat it consumes builds to roughly 2.0 to 2.5 mils dry film thickness and cannot be put back without a strip and repaint, which is five to seven weeks out of service.
Crew and hangar are the third factor
Short notice is dispatch work. Crew come off planned jobs, a bay is found at short notice, and the whole thing is staffed and priced as urgency. We run a 24/7 AOG dispatch precisely because aircraft do not schedule their own emergencies, and we will always take the next-morning call. But urgency buys speed, not standard. The only slot in which the full sequence runs in order is the one nobody is waiting on, and that is the argument for booking into idle time.
What changes the answer
A trip that appeared yesterday changes it. So does an AOG, a charter added at short notice, or a guest list that turned a positioning leg into a principal flight. In those cases the day before is the only slot there is, and the right move is to scope the work to what can be finished properly rather than start something that gets abandoned at dawn. Condition changes it too. Paint left long enough to need correction, or a cabin that has gone two years without a deep clean, is a planned job whatever the calendar says.