I flip flop a lot on wanting a second dog. Most days I am content with just Smiley, but other days I really want a dog that will play fetch with me, go swimming at the beach, and run around with reckless abandon. Smiley is just too reserved and self controlled in public, which is great most of the time, but I love having a dog that grabs life by the horns and is a little bit doofy.
I really want to get myself a puppy for my 30th birthday, but that's four years away. I definitely will not get a second dog before my parents' dog passes away. They dogsit for me, and are more than happy to, but they would struggle watching more than 2 dogs.
So, I guess my timeline would be in about 4 years.