Depends on your riding position. If you're leaning down on your bullhorns (simulating the brake hoods) and using them for out-of-the-saddle climbs, then no, it's not necessary to have long bar ends.

However, if your stem is especially low, or you have a pursuit geometry (sloping top tube), you can think of the bullhorns as drops, if there was a bar connecting the ends of the drops to which you could attach a stem, and as such longer bars ends make for something to grab on to while you're in that tucked drops position.

I guess generally, bullhorns are the actual bullhorn bars, while often "time trial bars" refers to the whole "aero" setup of bullhorns + slambars, but I don't know if that convention is followed very strictly.

If you're looking for something with more bar ends, check out the Nitto bars here.

Hope this helps.