Yes, the single task view does not give you "more options". I am opening the task from the email notifications.
After much trial and error, I managed to put the fields for start/due dates in that screen
In application/views/task/task_list.php, I just added the following piece of code to line 102
<div style="padding-top:4px">
<?php /*echo label_tag(lang('dates'))*/ ?>
<table><tbody><tr><td style="padding-right: 10px">
<?php echo label_tag(lang('start date')) ?>
</td><td>
<?php echo pick_date_widget2('task_start_date', array_var($task_data, 'start_date'),$genid, 60) ?>
</td></tr><tr><td style="padding-right: 10px">
<?php echo label_tag(lang('due date')) ?>
</td><td>
<?php echo pick_date_widget2('task_due_date', array_var($task_data, 'due_date'),$genid, 70) ?>
</td></tr></tbody></table>
</div>
Now when i hit "add subtask" the options for start/due dates are right there.