You can start at any time. I started at 29 weeks. I'll be 32 weeks on Sat. I've been drinking 1 cup a day. At 32 weeks, I'll probably up it to 2 cups a day. 3 cup/day at 34 weeks and 4 cups/day at 36 weeks until the end.
It's not a fruity tea. It's made from the leaf of the plant. If your tea is fruity, you're probably drinking raspberry tea and that's the wrong tea.
I drank it last pregnancy starting at 32 weeks and my labor was fast and I only pushed for 5 min, so it seems to me like it worked.