LeadPages does this, and it’s great. The idea is that a person doesn’t see an asset - particularly a button - until they’ve spent a certain amount of time on a page (or even on site).
Primary use case: Evergreen webinars / replays, to only reveal the button after the workshop is, say, halfway watched (so button appears under webinar after 30 mins time on page)
Hi there, @Joanna_Wiebe 
I see that you’ve already found our Button widget. Are you going to use the Embedded or Floating layout to display the widget after the certain time on page?
I noticed that you’ve chosen the Embedded layout and I guess the chances to implement for embedded button are not so high. This is why I wanted to ask you if the floating option works for you too 