The program I use suggested under 10 hours cutting time, but I tend to treat it's estimates with a pinch of salt. Most programs do not ask for an acceleration value when calculating the machining time, so either they ignore acceleration or use a typical value. For detailed 3D work like this the acceleration will make a huge difference to the feedrate, in addition to chances of the tool breaking.

I'll probably try various stepovers and see what it looks like. I'm not too bothered about the cutting time as it's not like I have to stand and watch it, but if it fits in a day that would be nice.

(2000th post, yikes!)