The side effect directions for it say do not take it close to bedtime as it could prevent you from sleeping.
I could not find anywhere a half life indication for it. However, if you have not been on it long, there should be no withdrawal effects. It is like adderall ( a stimulant) and should be out of your system fairly quickly. Of course, it does depend if you took the extended release version or not. Essentially, if you look at the label, the time it gives between doses plus half again should be a pretty good indicator that most of it is out of your system.
Note, under interactions, it says "Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially: ... other stimulants (e.g., amphetamines, methylphenidate, street drugs such as cocaine or MDMA/"ecstasy")." This is for a good reason, you are taking two stimulants. be careful and always look up any medication you take.
Hi! Your pharmacist would be a good resource for this question. We are not allowed to give dosage information on the site