You can change the date & time format in Google Sheets & Excel Online using this guide. Use different date & time formats in spreadsheets.

When you enter a date that's formatted with slashes, Excel will recognize it as a date. For example, Excel will automatically choose the date format for a cell that contains 11/11/19. You can set ...

While Microsoft Excel automatically reformats time values as hours and minutes, you can manually change the cell's time format to display the seconds as well.

Change the time formatting. Data tables that use the "h:m" time format will not export correctly to Excel. Click the column heading to select the entire column.

How to convert time values into decimal values in Excel Internally, Excel stores the time as a decimal value. The quickest way to see that time value is to change the format.