The 4-6 hour estimate sounds about right -- I am a slow (but steady) hiker and I think it took me 5 or 5.5 hours? I recall being slowed down by altitude that day. I was climbing with very little acclimatization and really felt it. You are probably quicker so figure nearer to 4 hours, assuming reasonable trail conditions? It is only 6.25 miles RT I think, most of which is on well defined use trail (summit pyramid is a little bit of a scramble).
I've only done Baldy from ski lift parking lot (this year) and that hut trail (last year). Dana is a much shorter hike, really apples and oranges. I've only done Whitney from the front side as a backpack. Dana is comparable in terms of vertical (but not mileage) to hiking to Trailside Meadow and back from the Portal. But shorter, steeper and far less switchbacking. It's a solid half day hike and it will give your calves a workout.
