You only get a few seconds after the end of the rebuy period on Boss to decide if you want to make a add-on or not.
So, the best way to ensure you don"t miss the prompt is to tick the "Auto Add-on" box as shown in the handy image below:
Likewise, if you"re going to rebuy anyway, you can check the "Auto Rebuy" button. Saves having to click "Rebuy" every time you go busto.
Important note: When you move tables, the software un-checks the boxes you have checked. So, when you"ve moved table re-check the boxes. (This is a known issue that will be fixed in a forthcoming update).