> For the complete documentation index, see [llms.txt](https://help.openloyalty.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.openloyalty.io/integrations-and-data-exchange/expressions/sample-use-cases/expressions.md).

# Elapsed Time Conditions

One way of keeping the customers engaged with the loyalty program is to occasionally reward them for taking some actions. The way to do it in Open Loyalty is to use an expression timestamp, which allows you to measure how much time has passed between certain events.

For example, you want to reward a user for purchasing items in your store in the first week after registering. <br>

To do so, you can create the following expression:

```
timestamp(transaction.purchasedAt) - timestamp(customer.registeredDate) <=  86400 * 7
```

The first part of the expression:

```
timestamp(transaction.purchasedAt) - timestamp(customer.registeredDate)
```

This means that you want to define the time passed between those two events: transaction and registration. In the second part of the expression, you define how much time passed in seconds. 86400 seconds is the number of seconds in a day, so <=  86400 \* 7 means that less than 7 days passed between two events.


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