Adult dose of valium is maybe 5mg at one time, possibly taken a few times a day depending on reason for prescription and severity of the indication or tolerance.
For oral medications, it generally takes 60-90 minutes for them to completely absorb. Metabolism is another thing. If the medication is ground up, larger surface area means faster absorption. Greater total volume also means your body will get more quicker.
With oral medications you can see an effect in 10 to 20 minutes when taken as directed. But obviously your method is different. Alcohol can potentiate benzodiazepines (including diazepam/valium), making them more "effective". This will probably also mean quicker significant effect.
There are a lot of variables. I don't know your weight, sex, digestive health, kidney or liver health, or medical history. That being said though, I would think that within 10 minutes you would probably be feeling *very* drowsy at least.