How long really depends on what sort of pond you want, how you'll be digging it out and dealing with the excess soil, if you have all the materials already, and if you can a little help.
If all you want is a hole in the ground with a liner full of water and you have all the material and a backhoe for an afternoon, you could build a pond in a weekend.
On the other hand, if you want a fully planted and landscaped pond with a nice waterfall and its own filter/pump room, and you plan to all the hand digging and wheelbarrowing all the soil yourself, you could be looking at many months with your schedule.
We built our pond inside a courtyard area that had to be built first. We started early in the spring and just got the pond full of water by the time it started to snow. Landscaping around the pond and the fish had to come the following year. We did all the digging and moving dirt around by hand. there was four of us but it was still a lot of work.
Here's a video of the progression.
It took me and a friend about 4 weeks to hand dig my 10 foot diameter, 2 1/2 foot deep pond. We only worked a couple hours at a time on some weeknights and weekends. And that was working around a week of rain and massive maple tree roots. Please post pictures of your progress - we love to see other people working!
I must admit, though, I too am having a problem seeing where you put all the soil from your pond hole if you already had that lawn there? Did you put it in the front yard?
