In Google Ads, click Edit on the campaign and open Times and devices.

On the left are the time ranges (Every day, Monday to Friday, Saturday and Sunday, or a single day, with a start and end). On the right is a grid of 7 days by 24 hours: click or drag to turn hours on and off, and click a day name or an hour to turn on the whole row or column. Above the grid you see the conversions (or the spend with no conversions) for each hour of each day, so you can decide based on the numbers.

Shortcuts: All times, Monday to Friday 8am to 6pm and Only where it converts (asks for confirmation and shows the amount spent).

Google's rules: minutes 00, 15, 30 or 45, up to 6 ranges per day, no overlap. You can't save with the whole grid turned off, because on Google an empty schedule means all times. Saving replaces the campaign's entire schedule, and it always shows the before and after for each day before saving.

The schedule limits when ads run under any bidding strategy. Bid adjustments by time range, however, are only available with Manual CPC, Optimized CPC and Maximize Clicks (see the article on bid adjustments by time or device, which may not appear with automated strategies).