It'll happen at any time. I got access to the Dream Suite project just today, but I'm still waiting for Blathers to ask me about a second floor for the museum. After waiting forever to get a painting to donate to the museum, I finally got one gifted from a neighbor, and now I'm painfully waiting for the museum upgrade request.
So these things are totally random. It may take you a while to get the Dream Suite like it's taking me a while to get the museum upgrade.
Opie & Anthony | Ron & Fez, XM 103/Sirius 206 XBL: Maxx the Slash | PSN: Maxx_the_Slash | 3DS: 3222-5637-7984 | Wii U: Maxx_the_Slash