Stardust Grind

8-10K per day is possible by grinding for two hours, catching everything, and walking a lot of km's with just the infinite incubator. If you are buying incubators, you can get more than that.

It's not really a lot of fun spending two hours catching every rat, sentret, and pidgey, though, just for the dust.

3 months, but I'm glad I have a go plus. My pokedex says I've caught 400 sentrets, 400 spinarks, and 200 Murkrows--that is 100,000 stardust!

Longer, than pogo will be relevant :D
Until you'll use go+ or grind few hours a day

You could do it in a week if you really wanted to! I did 40k last night. Maybe 4 hours. Probably closer to 3.

In my town, it is possible to catch two pokemon in a minute and spin inbetween, so the balls remain constant.

This would reward 12k dust per hour, a little more, if you catch evolutions.
In addition, there is some dust from the streaks.

Within 1 month you should be able to get your dust.