Normallly I`m working with the widget from andoid - so I add a task and then ? what will be the shortest way to add a reminder with date and time ?
Unfortunately, there's no way to set an absolute reminder for a task while adding or editing it through the widget. You would have to use relative reminders instead as every time you set a date and a time for the task, for example - every day at 2pm, it would get a "30 minutes before deadline" reminder added automatically to it.
We'll consider changing this and expanding the task adding menu on the widget in future updates.