Hello,
The tolong() function in Kusto Query Language (KQL) is used to convert a numeric or datetime expression to a long integer (Int64). In the context of your provided query, it's being used to convert the impactstarttime value to a long integer and check if is greater than 1.
https://learn.microsoft.com/en-us/azure/data-explorer/kusto/query/tolongfunction By example : | where tolong(impactstarttime) > 1