Working from this: ...dynamic clock or meteo widget on the page could boost the SEO... ...has been updated with new content.
Short answer? No. Not even close.
Search engines, using more than one page, can determine patterns within the HTML DOM model that separates the header, footer, sidebar, and any other page element that is truly not content. The idea is to evaluate the content and not things that do not add value to the content directly.
Let's assume for a moment, that the "clock" is within the content itself.
Search engines do not look at content in a linear way. It can't. Computers do not read and cannot evaluate what they see in a way that humans can. For this reason, the evaluation of the content uses semantic analysis including semantic topic scores, semantic linguistics, and others to evaluate the content itself. What Google, in particular, sees would be small changes in content scoring if at all. These methods adequately handle restructuring and reordering of content, spinning content, keyword stuffing, content gibberish, and any other trick that was designed to deceive search engines.
Content has to have meaning. Adding erroneous elements that do not add meaning do not add value. It is that simple.
For content to be fresh, there are several factors that are in play. One is whether or not new content is update routinely. Another is whether older content is updated periodically as appropriate. Another still is how factual a page is as compared to other content on the web. There are quite a few metrics that determine freshness. Not every page has to be updated to be considered fresh. Relevance and search engine result page (SERP) performance is a factor too. Freshness is not simply updating a page. It is a series of metrics site wide that determines if content is fresh.
As a warning, please do not follow the advice of junk SEO sites. There are too many of them. There are no tricks that work. Any SEO advice that is even hinting at an advantage outside of creating compelling, well written, sought after, and well structured content is very likely leading you down a very foolish path.