When an experiment starts, metric cards are calculated every 15 minutes. You can see the last time the metrics for an experiment were calculated under Summary of key and organizational metrics on the Metrics Impact tab.
The duration between updates scales with the length of the version. We do this because, for example, on day 5 the traffic for the previous 15 minutes is not likely to show a material difference. The time between calculations increases incrementally through the duration of a version. It will typically be an extra 1-2 hours per day between calculations. Though, depending on timing on the back end, if a split has been running for more than 12 days, it can be up to 48 hours between calculations and up to 72 hours after the version of a split has been running for more than 48 days.
We have it on our roadmap to provide an ETA for next calculation for any experiment you are running. In the meantime, you can send a request to support for Split to manually run a calculation.
In addition, as a best practice you should establish experimental review periods. Making conclusions about the impact of your metrics during set experimental review periods will minimize the chance of errors and allow you to account for seasonality in your data.
Perhaps, you see a spike in data on certain days of the week. It would be against best practice to make your product decisions based on the data observed only on these days. Or the key event, such as arriving for a restaurant reservation, may not happen until a few weeks after the impression.
We will always show your current metrics impact, but discourage you from making conclusive product decisions outside of review periods.
Experimental review periods are a common practice for sophisticated growth and experimentation teams. For some experimentation teams, no decisions can be made until the experiment has run for a set number of days.
This article provides more information on reviewing your metrics cards.