i had drank it when my baby 16 weeks since my father has 糖尿. it need around 2 and a half hours, before u drink 糖水, nurse will 抽blood, then, u drink 糖水, and wait for 2 hours, nurse will 抽blood again. then u can leave....so i suggest u better bring some bread or biscuit, after finish all the process, u can eat immediately....