Open web page at a specific time of day; or after 8 hours of activity

Going off your original comment, you can achieve the above using Task Scheduler.

On Task Scheduler, right-click on the Task Scheduler Library and choose Create Basic Task

• The first step is pretty trivial - Give your task a name and description.

  

• You want it to run daily, so you don't need to do anything for the next step.

  

• On the next step choose a starting date and time and how often you want the task to repeat.

• On the Action stage of the Wizard select the Start a program option. This is where you will need to specify the location of the application (Google Chrome) you want to execute and any additional parameters. Specify the website you want to open in the Add arguments section. As an example I've used http://www.bbc.co.uk/news

  

Once that is done, click Next and then Finish. Google Chrome should now open at the specified time every day and it should load the website listed in the Add arguments section.

Additional Notes: If you can't find where Google Chrome is located, right-click and go into its properties. On the Shortcut tab, the Target field is what you need.

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From the comment by @TravisHeeter

You can also use a "Weekly" trigger to have the task run on week days:

Also, for any scheduled task to work, you may have to restart your computer. You can test your task after it's created:

Make sure it's selected in the middle column, then click "Run":

If nothing happens, your task didn't work, and a restart should be considered.

While I appreciate the original answer, I have since found the "Tab Snooze" and "Cron Tabs" extensions useful. The former is what I currently use, as it has a "periodically" feature to have a website open up every weekday.