Timescales in the Web App's Power Meter are currently limited to 15 minute, hourly, daily, weekly, monthly, and yearly. You can scroll to zoom and drag to move forwards and backwards in time, but occasionally you may want to access a custom timescale instantly. You can do so by making some simple modifications to the page's URL.
Navigate to your address bar. You should see a URL similar to the image below.
There are two important sections here: the Start and the End. Within these, there is a date field and a time field (24h, local time). To customize your Power Meter timescale, all you need to do is modify these to your own Start and End times.
If I wanted to see the past six months (and today is August 7, 2019), I'd use the following URL:
If I wanted to see just the past two weeks, I'd use:
If I wanted to see just the past six hours of the same day, I'd use: