I'd say if finances are what seems to be holding you back, then once you feel like you can handle the extra cost of a second and you still really want a second dog at that point, that's when to do it
Just consider your current dog when that time comes, if your dog is a little older or really mellow, you may not want a puppy, as that could be too much, or maybe not, you know your dog best
For us it was always a breed thing, I had my beagle since I was 19, when we bought our house, dh wanted a large breed since we now had the room so we got our Akita. Recently, I was really wanting a toy breed for a long time, so when the opportunity came along to get Alice for free, I jumped on the chance.
