Since when; from what time; asking when something began (or how long something has been the case).
いつから日本語を勉強していますか？
Since when have you been studying Japanese?
これ、いつから料金が上がったの？
Since when did the price increase?
彼女はいつからそんなに料理が上手になったのか不思議だ。
I wonder since when she has become so good at cooking.