I have a 9 to 5 job and have been developing my Kickstarter on the side.
I spent likely 15-20 hours a week for about 3 months developing my product and doing things such as building a launch email list, price sensitivity analyses, and landing page building.
The week of our launch, I took vacation off work (my 9 to 5) and worked bout 16-18 hours each day the entire week of our Kickstarter launch (we launched on a Wed).
To put it in context, it was me and another business partner who launched our Kickstarter product. I probably worked ~50% more than he did on the project.
But gives you and idea so you can plan your time launching your own project accordingly.