[Feature request] Time Since option for choices (Similar to TURNS_SINCE)

Hello!

I would like to request a feature that might be cool to add. There should be a way to make specific choices appear after a certain amount of time, along with other uses. Like, if a player waits for 2 minutes without picking a choice, another appears and they can pick that. I think it would be similar to TURNS_SINCE, but like TIME_SINCE.

For example...
```
===first_knot===
* [normal choice] -> knot
* [also normal choice] -> knot
* {TIME_SINCE(-> first_knot) = 00:02:00} [secret choice] -> knot
```
(The 00:02:00 would mean 2 minutes)

I think it would be cool to see. Thanks.