till. Here with Greek "an", and the Subjunctive Mood, marking the uncertainty, which was conditional on the repentance of the nation. Note the four "tills" (Mat_10:23; Mat_16:28; Mat_23:39; Mat_24:34), and compare what is certain with what is uncertain.
be fulfilled = may have begun to arise, or take place: referring specially to the first "sign" in Mat_24:4, in response to the first question in Mat_24:3; not the same word as in Luk_21:24, but the same as in Mat_24:32.