How to make a button active only after certain time?

Civer over an interactive object is an outdated technique which will for sure never work for HTML output.

The Delay command as mentioned is a possibility but you have to know that the timer is not taking into account anything. Example: if the learner pauses the slide for some reason, the Delay timer will not be paused at all.

You didn't give much details, but if possible, setting this up in the timeline is always the best method. Do you need to see the button while it is inactive? In that case use an image during the inactive part and the button in the active part. If it is a shape button that is perfectly possible.

You could make an Advanced Action to execute onEnter that would disable the button and then, after a designated delay - enable the button.

Alternatively - you could make the button hidden at the start and use the same delay idea to show the button which will have the same effect other than the button will be seen on the stage in the first example.