To prevent YouTube links from losing their start time when posted on forums like Physics Forum, users should format the link correctly. Instead of using the standard format with "&t=63s," the alternative format "/vidname?t=nn" is recommended, where "nn" corresponds to the desired start time in seconds. This method ensures that the forum's media HTML conversion does not strip the start time. Additionally, posting the link with accompanying text can help maintain the intended functionality. Proper formatting is essential for preserving the start time in shared links.