Spreadsheet widgets powered by a Google Sheets spreadsheet automatically refresh within 3 minutes from the connected spreadsheet's last update.
.xlsx files uploaded to Google Drive, Dropbox, and OneDrive the refresh rate is around every 15 minutes.
Refresh rates when using import formulas
Widgets powered by import functions, such as ImportRange and ImportData, automatically refresh around every 15 minutes. Be aware, though, that when data from multiple import functions with their own refresh intervals are used in the same connected spreadsheet, it can affect the accuracy of the data displayed.
If this isn't fast enough for your needs, you can set your own refresh interval by writing a script using Google Apps Script Editor.