In this case, 会議は一時半まで終わると思います isn't correct, it should be 一時半までに and adding は emphasizes the time like "at least until at 1:30". *You can say 会議は一時半まで続きます / かかります, it means "the meeting will be continued until at 1:30" in the literal translation. I hope my English isn't bad and this helps you.

Usually the first "は" is a topic and the second（and the third, the fourth, ～） is contrastive or avoiding other possibility. "会議は一時半までには終わる" means "The meeting will end by 1:30（not by 1:00 or not by 2:00 or not ～）". Another translation is "The meeting will end at 1:30 at the latest." "まで" means "till/until", so when you use it, the sentence should be like this "会議は一時半まで続くと思いますよ。" means "I think that the meeting will continue till 1:30".