Recently, some logs had the date and time in UTC itime format. Wanting to convert it to something more human usable in Google Sheets, the following formula seems to convert 1604428241 to 11/3/2020 13:30:41. The formula is:

=(((A1/60)/60)/24)+DATE(1970,1,1)-TIME(5, 0, 0)

where A1 contains 1604428241. Remember to format the cell(s) appropriately.