initial commit

_bmad-output/implementation-artifacts/4-2-time-math.md

@@ -0,0 +1,47 @@
+---
+epic: 4
+story: 4.2
+title: "Time Math"
+status: draft
+---
+
+## Epic 4 — Date, Time & Time Zones
+**Goal:** Full date/time math, business day calculations, and timezone awareness.
+
+### Story 4.2: Time Math
+
+As a CalcPad user,
+I want to add and subtract durations from times and calculate durations between times,
+So that I can compute meeting end times, elapsed time, and scheduling math.
+
+**Acceptance Criteria:**
+
+**Given** the expression `3:35 am + 9 hours 20 minutes`
+**When** the engine evaluates it
+**Then** the result is `12:55 pm`
+
+**Given** the expression `3:35 PM + 9 hours 20 minutes`
+**When** the engine evaluates it
+**Then** the result is `12:55 AM` (next day)
+**And** the result indicates the day rollover if applicable
+
+**Given** the expression `14:30 - 2 hours 45 minutes`
+**When** the engine evaluates it in 24-hour mode
+**Then** the result is `11:45`
+
+**Given** the user's time format preference is 12-hour
+**When** time results are displayed
+**Then** they use AM/PM notation
+
+**Given** the user's time format preference is 24-hour
+**When** time results are displayed
+**Then** they use 24-hour notation (e.g., `14:30` instead of `2:30 PM`)
+
+**Given** the expression `9:00 AM to 5:30 PM`
+**When** the engine evaluates it
+**Then** the result is `8 hours 30 minutes`
+
+**Given** the expression `11:00 PM to 2:00 AM`
+**When** the engine evaluates it
+**Then** it assumes the time crosses midnight
+**And** the result is `3 hours`