When on synthroid (thyroxine) and adderall what is a safe time between taking them to avoid any interaction?

Any time: There is no interaction between synthroid (thyroxine) and Adderall per se. If you take them together and notice new side effects - tremors, heart beating fast, mind racing - then spacing out your doses by 4-6 hours or so should help eliminate them.

In a perfect world: You would take your synthroid (thyroxine) an hour or two prior to your adderall. Remember, you should avoid taking your synthroid (thyroxine) with diary and/or mineral supplements too. Overall though, there really isn't any significant interaction between the two medications.