A burn test of these fuel cubes I made yesterday gave me an astonishing 23.5 minutes.
For camping or survival, this is fine. As an ultra lighters cooking fuel, its overkill. Today I made another tray of cubes, a little smaller.
Other notes from this burn test:
Use the bottom of a soda can stove, with enough clearance to your cooking pot. These cubes were a little tall for my initial arrangement, which meant my pot smothered it a little. That eventually righted itself when the cube burned down.
I will cut a soda can down for this sole purpose, and can burn it inside a single layer aluminum can. One inch tall should be about right.
Take care the wax doesn't melt and overflow the well, which can put a burnable substance on the shelter floor or your camping area. For that reason, I'd move dry leaves, grasses or duff away from this stove as well as any other stove.
Several sizes of cubes would come in handy depending on the needs. I haven't tried to extinguish one and then relight it, but that should work if necessary, if enough wax is left to hold the cube together.