I'm wondering if there's an open source license like GPL but lets you sell a program/product for a specific amount of time. Then, after a reasonable amount of time, say 1 year after product release, convey the source code for that product with the same license.
No, that is a matter of steps that you take.
Finish your product and sell it, while keeping the source to yourself. Once you want to make it open source you then make the source available under whichever license you choose.
As the sole copyright owner you have no restrictions in this regards. If you have other contributors, they will each need to agree to this. I expect that legally it would be best if you added any open source licensing terms to your code at the time you release it under those terms and have no more than a copyright notice while you are releasing it as a closed source program.
If you are incorporating code from another project, then you will need to adhere to any of their licensing terms from the start.