The short answer is; we can’t actually answer that. Partially because we’re not medical experts, and partially because there isn’t a single answer to either of those questions.
Speed of onset will vary wildly based on how the sedative was administered and what the dosage was.
Side effects will be determined by the sedative and the sedated. Honestly, there are a lot of different sedatives, and every single one has a list of side effects that pop up with some patients and not with others. Hell, what the sedative even does will vary.
If you’d given me a specific drug, I might know off the top of my head, but, again, we’re not medical experts, for this you’ll actually need to talk to a doctor or a pharmacologist. An anesthesiologist might work in a pinch if you know one.