can i go to taizhou (zhejiang) from guangzhou by train, how long will it take.

There is no train between the two places. If you really want to take the train, you need to transfer in Wenzhou.
There is only train from GZ to wenzhou, K326/K327. The train takes almost around 23 hours.
The bullet trains from Wenzhou South railway station to taizhou costs around one hour.

In my opinion, the direct flight between the two places are suggested.