cacheLifespan

Time in hours during which you want to keep your data before it is fetched again.

Google Sheets controls how the functions recalculate according to different behaviours (modifying cells, opening the spreadsheet, …)
To avoid that IMPORTFROMWEB fetches the data source constantly, the content is cached 24 hours by default. Therefore, whenever IMPORTFROMWEB recalculates, the content is retrieved from the cache.

You can customize the cache lifespan by setting the cacheLifespan option to the number of hours you want the cache to last.

=IMPORTFROMWEB(data_sources, selectors, "cacheLifespan:48")

or

AB
1cacheLifespan48
2
3=IMPORTFROMWEB(data_sources, selectors, A1:B1)

Bear in mind that the function will not necessarily update directly after the cache expires but only when Google Sheets lets the function recalculate.

A new request will be counted whenever the function has to fetch the content from the data source.

cacheLifespan is available from the Premium plan. The maximum value for cacheLifespan depends on your plan: 15 days (360 hours) for Premium, 30 days (720 hours) for High Volume.

Other ways to control how your data is updated:

Use automatic triggers if you need the function to update periodically.
See Set up automatic updates

Control the cache lifespan for all the functions in your spreadsheet through the sidebar
See Use the sidebar