Here are a couple Chrome extensions, you can use in Opera, that gives you an eye rest warning.
https://chrome.google.com/webstore/detail/eyecare-protect-your-visi/eeeningnfkaonkonalpcicgemnnijjhn
https://chrome.google.com/webstore/detail/eye-rest/mndlfpadbgecofachcbpndicbefbonfm
There's an Opera extension called Super Auto Refresh that would appear to let you refresh pages and tabs. https://addons.opera.com/en/extensions/details/super-auto-refresh/?display=en
And here's a Chrome extension (you can use in Opera), where you can set the number of seconds you want to pass before a page or tab refreshes.
https://chrome.google.com/webstore/detail/easy-auto-refresh/aabcgdmkeabbnleenpncegpcngjpnjkc
Remember, to download a Chrome extension easily, you need the Opera extension, called Download Chrome Extension, https://addons.opera.com/en/extensions/details/download-chrome-extension-9/?display=en
or Extension Source Viewer, https://addons.opera.com/en/extensions/details/extension-source-viewer/
Hope some of this helps you.