The timer keeps running if you close the tab, and every entry is kept on this device. Nothing is uploaded and there is no account.
Rounding the way you bill
Many freelancers bill in steps of 6 or 15 minutes. Pick a step and whether to round to the nearest step, always up or always down. Each entry is rounded on its own, the same way most billing software does it, so the totals match what you send.
From hours to an invoice
Pick a client and dates to see just that work, then press Add to invoice. The invoice maker opens with one line per project, day or entry, the hours as the quantity and your hourly rate as the price.
Keeping a copy
Entries stay in this browser until you delete them. Export a CSV now and then to keep a backup, or to open your hours in a spreadsheet or send them to a client.