Get current current trigger time in automation

I want to write an automation that when should log the time between two scans of the same tag.

So when to automation will run in single mod and be trigger by a NFC tag scan, then it will wait until that tag have been rescanned or timed out in 3 hours.

I would then like the fetch the amount of time between the two scans. How ever i cant seem to figure out how the get the timestamp of when an event was fired. Alternatively i cant seem to find a way on how to store a value in a variable since then i could store current time into two difference variables on each scan and then just calculate the time difference.

If i have got this working i will also then have a follow up question on how to replace input to call services from being hard coded now using my calculation or custom variable

It’s a lot easier if you show us what you have currently. Even if it doesn’t work it will still be something to base everything on.