This function auto adds a date on a specific cell after a specific cell is filled out. In the code below, "Main" can be replaced with the name of the tab.
function onEdit() {
var s = SpreadsheetApp.getActiveSheet();
if( s.getName() == "Main" ) { //checks that we're on the correct sheet
var r = s.getActiveCell();
if( r.getColumn() == 1 ) { //checks the column
var nextCell = r.offset(0, +2);
if( nextCell.getValue() === '' ) //is empty?
nextCell.setNumberFormat("MM/dd/YYYY")
nextCell.setValue(new Date());
}
}
if( s.getName() == "Main" ) { //checks that we're on the correct sheet
var r = s.getActiveCell();
if( r.getColumn() == 11 ) { //checks the column
var nextCell = r.offset(0, +2);
if( nextCell.getValue() === '' ) //is empty?
nextCell.setNumberFormat("MM/dd/YYYY")
nextCell.setValue(new Date());
}
}
}