The actual Amount has more resolution than the value you see in the display. Between 0% and 1% there are more values - you need a very fine hand, adjusting the Amount with tiny and slow moves.
Also, if you want to control that even more precisely, and/or you want to have manual control over it, you can use the mod wheel (or other controller) to modulate the mod matrix cell that does the BBD delay (hold column 1-8 and press that cell to s3et up that mod destination). That'll give very fine control, and the mod wheel position is stored with the patch. Or if you want dynamic control in the patch, e.g. an envelope can be used for fine and varying control of that same cell.