It takes about 5 half lives to clear 95% of a substance from your system. A quick google says the half life varies from 5-21hrs, so even if you’re on the slower end, a week should do it.
If you’ve been on it for a very long time then your CNS may need more time to get back to baseline, but you probably don’t need a perfectly clean slate to assess if a new medication works for you. Plus, switching from a nonstim to a stimulant is a totally different class of drug and you should feel the effects of a stimulant fairly quickly.
Just make sure you time and dose correctly to avoid messing up your sleep.