You can get the timestamp and add it when you append the new row. Something like this:
function myFunction() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var source = ss.getRange("AppFormt!C5");
var destSheet = ss.getSheetByName("Sawmill MBF Per Hour");
destSheet.appendRow(
[ new Date(), source.getValue() ] ); //put both values inside an array
}
You might be able to condense it down further, but then it gets difficult to follow what you did a year from now.. lol
function myFunction() {
var value =
SpreadsheetApp.getActiveSpreadsheet().getRange("AppFormt!C5").getValue();
var destSheet =
SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sawmill MBF Per Hour").appendRow( [ new Date(), value ] );
}