Tweak once it does not matter what your taking. It just depends how your body chemically interacts and metabolizes the product your taking. Furthermore, that is why there is such a wide range of times a drug will be effective. For one person it may be 8 hours for another it is 2. Therefore, they usually say 3-5. Personally, if i take any amphetamines I cant sleep for at least 8 hours after the consumption. (waah )
Oh on the Wellbutrin there is really no side effects to taking both. In fact, at my pharmacy the patient sometimes uses both. Therefore, there will be no effect. Furthermore, your Fish oil and multi-vitamin is mostly water soluble.
(Source Pharm Tech) Hope that helps you!