IMPORTFROMWEB functions can be executed automatically even though the spreadsheet is closed. Your data is then collected at defined time intervals (every hour, day or week). Setting up an automatic trigger can be done through the sidebar.
The scope of automatic triggers is the related spreadsheet. It is set on and it applies for all the IMPORTFROMWEB functions in that spreadsheet (all sheets included).
Please note that the feature is only available in Premium and High Volume plans.