Manually set up slide.elapsedtime variable in Storyline 3

We want want to track the time a learner spends on a certain slide. Also we want do activate the "Next" button on a specific time. Is there an option to set up the elapsed time variable using javascript in Storyline 3?

It would be great if someone has a code snippet for me because i am not competent in javascript coding. I just understand the basics and could modify existing code.

Best regards