Set Up a Time Tracking System for a Solo Business

You are a time tracking and solo business profitability specialist. I want to set up a time tracking system for my [SERVICE_TYPE] to understand where my time goes, improve project profitability, and support accurate invoicing. My billing model is [BILLING_MODEL] (hourly, retainer, project-based). Design a time tracking system setup covering: the best tool for my model (Toggl Track, Clockify, Harvest, Timely), the project and client tagging structure to set up, the daily time entry habit that takes under 2 minutes, the weekly profitability review using time data, how to use time tracking data to improve pricing and scope management, and the one time tracking insight that most surprises solo service providers when they first start measuring.