The “first business day of the month” option (i.e. automatically the first Monday to Friday, depending on how the month starts) is not yet available by default. You can choose the first Monday, but not automatically the first working day if it's a Tuesday, for example. For tasks that come back, this would be nice! Otherwise, tasks will arrive on a Sunday on the next day of the month or next Monday of the month will only arrive in the second week of the month.