^^^
If you were driving, without traffic, from the North End in Boston to Newton, it would probably take about 20 minutes or so. No idea what it may be like in rush hour traffic.
I grew up in Newton and often took the Green Line D train into Boston, and it took a long time...maybe not an hour but much longer than it should have because instead of going directly from Newton into Boston, it winds its way through Brookline and makes a lot of stops. I'd assume that if someone was talking about public transportation that this is how they'd recommend you go, but I'm not sure how far the closest stop may be from GB Boston through. If there is a way to take an express bus that may be faster, but I'm not sure where those stop in Newton other than Newton Corner; maybe you could connect to another T bus from there.
Maybe one of the GB Boston guys can recommend a faster route.