Add Hour-Based Duration & Accurate Time Calculation

Summary:

Duration currently works only in days and counts the start date as Day 1, which causes incorrect due dates.

Example:

Start: 16-Apr-2026 15:00

Duration: 2 days

Expected: 18-Apr-2026 15:00 (48 hrs)

Actual: 17-Apr-2026

Request:

Support duration in hours

Calculate due date based on actual elapsed time

Add toggle for Day-based vs Time-based duration