Calendar Pro
Calendar already records the hours you actually work on each event. Calendar Pro turns them into a weekly or monthly timesheet by project - export it as CSV or print it - and into an invoice: your rate, VAT if you charge it, your details and the client's, and the next invoice number, printed or saved as a PDF. Pounds by default, other currencies too.

Edit an event and fill in Actual duration (hrs) as you go (free).
··· > Print & export > Timesheet: a week with a column per day, or a month with a column per week, by project, then every event.
Export CSV for a spreadsheet, or Print / Save as PDF.
Make an invoice (or ··· > Print & export > Invoice from hours): pick the dates and project, your rate, the currency and VAT. Calendar remembers your details, the client and the next number.
Print / Save as PDF - choose your printer, or Microsoft Print to PDF.

Timesheets and invoices help has every option in detail.
Part of Calendar Pro. Calendar is free. Calendar Pro is a one-off £5.99 upgrade inside the Windows app, bought through the Microsoft Store - no subscription, no account. Try it free for 7 days.
Yes - tick the planned hours option and events with no actual hours count at their planned length.
If you tick Add VAT, at the rate you set (20% by default). It's a simple invoice - check it meets your own accounting needs.
Pounds by default, and euros, US dollars, złoty and Swiss francs, shown the way your PC formats money.

Day, Week, Timeline, Month and Agenda - drag to reschedule, week numbers and UK bank holidays.

Tag events by project, filter to one, and log actual hours against planned.

Notes for every day, exported as a formatted site diary for any date range.

Windows notifications before your events, even when Calendar is closed.

Day, week, month and year wall planners in three styles - print or PDF.

Every event for a project, planned against logged hours, with CSV export.

Diary entries, weekly update emails and project summaries - private, on your PC.

Midnight, Graphite, Forest, Plum, Paper and Ocean.

All twelve months at once, with event dots - click a day to open it.

Bank holidays for Scotland, Northern Ireland and Ireland, and the clock changes.

Everything in one file - restore with a preview, merge or replace, and undo.
Calendar is free, in your browser and on Windows. Calendar Pro is a one-off £5.99 in the Windows app, with a free 7-day trial.