I cannot give the number of weeks it will take your plumeria to root because it varies with different varieties. Some plumeria are fast and may pop out a healthy clump of roots in 3 weeks. Others sit there for a spell and after that, they sit for another spell. I have seen some take over 6 months to root, but that is not common. Plumeria root the fastest in late spring through the summer.
Heat is important.
Here in Texas most plumeria root during our summers within 4 to 6 weeks. Some of our customers want only rooted plumeria, and for whatever reasons, they will have nothing to do with unrooted stock. This is fine, only please understand we only allow patient people to order rooted plumeria. When we receive an order for a rooted cutting, we check to see if we have any rooted stock ready to go. We pot that cutting and we wait.