I'm not sure how we could possibly be able to answer this - we aren't you, we don't know your experience with benzodiazepines or lack there of, etc.
2.5mg is a tiny dose - it may produce some very mild sedation (unless you're hypersensitive) but if you have no experience with benzos, it's not going to do much. You might not notice any effects or they might just be in your head. To put it in perspective, a standard dose of tylenol PM or benedryl would be more sedating than 2.5mg of diazepam.
Maybe you're a tiny person who is ultra-sensitive to diazepam and this will knock you on your ass, maybe without my post you would've had a strong placebo effect and would have been knocked out in 3 minutes... there's no way to know.
You're asking us to be fortune tellers and not even giving us any information that we could make anything resembling an educated guess off of. I apologize if this is coming off as harsh, but this forum has had quite a few of these type of posts essentially asking us to be psychics.