You’ll have to use a timer helper and start that running from the automation.
Edit: You might also turn the floodlight off with another automation triggered by the timer finishing. This would avoid having a long delay in the first automation.
Be advised that if you modify your automation to use a timer entity, not all cards are able to display a timer’s remaining time. I know an Entities card can. If you intend to use something other than an Entities card, you should confirm it can display a timer’s countdown (before you start redesigning your automation).
See here in the config docu of timer-bar-card. That should do what you expect, but it only works on a frontend basis, meaning it only mirrors the delay you set. They are not in any way connected, so if you eg. change the delay in the automation, you also need to change the duration in timer-bar-card.
If that’s enough for your use case, I can recommend the card. I’m using it for a few months with no issues to report.