It depends on if I have an idea for the level. If I have a clear mental image of how I want the level to look, I can make one in 10 minutes. On average, after tweaking, and route-adjusting, it usually takes between 30-90 minutes for the original design and another 30-60 minutes to tweak the level, remove backroutes, etc.
I'll review Hubbart 4.2 soon as I can find and load it.