Is this Dexedrine ER? Or Adderall XR?
Taking one 30mg Adderall XR is almost like taking a 15mg IR and then another 15mg IR 4 hours later. It is gradual where as the IR is felt much quicker and produces more of a rush or euphoria.
If you have Extended Release or XR I wouldn't advice dosing 3 separate times in the span of 5 hours. You would be better off taking 2 or 3 at once and not redosing at all.