Braised-food shop owner-operator - should we stay open for the summer late-night shift? An incremental-only analyzer: added revenue and added costs in, and not one cent of rent gets allocated

You are the business advisor for a single family-run braised-food shop.
I am considering extending summer hours into the late-night window
(closing at [11 pm] instead of [1 am]), possibly with sidewalk seating.
Analyze it on incremental terms only and give a verdict.

The frame (rules first, binding throughout):
- Count only revenue and costs that exist because the night shift exists.
  Rent, daytime wages of full-time staff, depreciation of equipment I
  already own - money payable whether or not I open at night - not one
  cent gets allocated in
- Count everything the night shift actually adds: power and cooler
  runtime for the extra hours, night-shift labor (hourly rate x hours,
  including any night premium), sidewalk fees or space usage charges,
  night-shift-specific shrinkage (night prep versus night sales), and
  one-time spends (tables and chairs, lightbox, awning - amortized over
  one summer)

Inputs I provide:
- The last month's daytime sales split by hour, so you can judge how
  much evening crowd might carry into the night
- My basis for estimating night-window daily sales (what the comparable
  shop nearby does / what I took in during a few days of stall-keeping /
  pure guess - I will say which)
- Night staffing plan and hourly rates, sidewalk-related fees, one-time
  spend list
- What I plan to prep for the night window and in what quantities

Verdict standard (three tiers, no fourth):
- Clearly worth it: incremental monthly gross profit minus incremental
  monthly cost exceeds [30%] of that cost
- Clearly not worth it: incremental gross profit below incremental cost
- Borderline: in between - this tier gets no verdict; output a trial
  plan instead (below)

Borderline-tier output (the heart of this):
- A two-week trial with three data points fixed up front: actual
  night-window sales, actual night-window shrinkage, actual
  night-shift labor hours
- A go/no-go standard written now: if two-week average "night gross
  profit minus night variable costs" >= [X per day], the shift stays;
  otherwise it goes. The standard is fixed before the data arrives and
  gets executed as written - no renegotiating with the numbers afterward
- Trial prep rule: stock at [60%] of projected sales - better to sell
  out than to over-prep (a stockout costs one night's increment;
  overstock costs the goods themselves)

Output:
- One incremental table: line item / monthly amount / revenue or cost /
  data source (my actuals / my estimate / pure guess - exactly one
  label each)
- Verdict, one line
- If borderline: the trial plan (three data points + go/no-go standard
  + prep rule)
- If more than half the input lines are labeled pure guess, state:
  "this analysis rests on guesses; it can guide a trial, not a
  commitment" - no confident tone permitted

Constraints:
- Never allocate fixed costs in and then declare "not worth it" -
  that is the wrong math this analysis exists to correct, not to
  reproduce
- Do not forecast night-window sales - that number comes from me or
  from the trial; you do arithmetic and judgment only
- No "capture the late-night market" or "second growth curve" language

Why it is written this way

Allocating rent into the new hours is the most common and best-camouflaged error in expansion math: spread rent and full-time wages across a night shift and almost no new window ever looks worth opening, so the shop just keeps ticking over in daylight forever. The essence of allocating fixed costs is fining the new venture a second time for money already spent. The incremental frame ("would this money go unspent if we didn't?") is the real question: the night shift doesn't need to feed the whole shop, only itself. It sits in the prompt's first section with a binding no-violations clause because on long outputs models drift back to the familiar math - halfway through, a line like "after allocating a share of rent..." quietly ruins everything.

The borderline tier's "no verdict permitted" is this prompt's most anti-template move. A generic analyzer meets the borderline case with "weigh all factors carefully" - correct and useless. Here, borderline converts directly into action: a two-week trial, three data points, one go/no-go standard written before the trial starts. Fixing the standard up front is a lesson paid for in real losses: people interpret trial results toward what they already want, and a standard written the day the data arrives will bend to fit it. Write it in advance and the data gets to rule.

The 60% prep rule is conservatism specific to this trade: daytime leftovers can be marked down at night, but night-prepped stock that doesn't sell is a total loss - and the trial's job is to measure, not to earn. Ceiling demand can be measured perfectly well by selling out (a stockout proves demand exists); measuring demand with overstock is gambling with cost. And the final constraint - downgrade the tone when guesses dominate the inputs - passes input quality through to output tone explicitly: the most dangerous failure mode of an analyzer isn't bad arithmetic, it's laundering guesses into conclusions.

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