You can easily monitor your ImportFromWeb usage from your account tab on the sidebar, where you’ll find detailed information about your request count and remaining quota.

Current user: has to be the same email as the spreadsheet owner.
Current period start: indicates the first day of the current monthly cycle
Requests used during period: the number of requests that have been executed in the current monthly cycle out of the total requests available.
Daily request limit: the number of requests that have been executed in the current day out of the daily quota.
Total requests used: the total number of requests ever executed.
To see a detailed log of your requests, click ‘Show requests from current period”.