You can use onblur event of start time field, and invoke a JS function that will change the end time (using jquery or plain js).
Refer faq: Q) How to populate other column, based on previous columns.
http://phpgrid.org/faqs

I tried that code and put an alert(); into the function.

When I entered the cell and/or left it would never fire.

I looked at some other previous posts and the above does not seem to support inline editing correct (or has that changed)?

Do I need to do the ExcelView integration to have this work with inline?

I was trying to get it to work just by editing the record in the edit view (similar to the add view).

Thanks – Greg

In any demo, e.g. demos/appearance/group-header.php you can try adding following line:
$col["editoptions"]["onblur"] = "$('#company').val( $('#name').val()+' company' );";

It will auto set company field onblur of name field.

$col = array();
$col["title"] = "Name";
$col["name"] = "name";
$col["editable"] = true;
$col["width"] = "80";
$col["editoptions"] = array("size"=>20);
$col["editoptions"]["onblur"] = "$('#company').val( $('#name').val()+' company' );";
$cols[] = $col;